Firstly which H190 are you using because there were in order quite a number all different to a degree but all needing different setups because of that.

Firstly datsun 2000 Sports,Width OK 25 spline axles imperial fittings not metric.LSD available,Alloy diff centre carrier.

Next was the Datsun 1600 wagon similar to above but metric also 25 spline axles just like a 1200 Ute.
Width useable stock under a 120Y maybe 1200 with correct wheel offset ie Front wheel drive rims like a laser early model.

Next was the 620 ute diff width useable stock just like the 2000 sports,These along with the later 720 Ute diff ran large diameter tapered roller wheel bearings with shim adjustment and the axles used a thrust face inside the diff centre.
25 maybe 30 spline axles,Can't remember exactly and the ability to setup the axles with zero endfloat made them ideal for use with rear disks as they had zero pad knockback.
Used the Alloy centre like the 2000 sports.

720 ute 30 spline axles ideal candidate for a wider vehicle cast steel carrier bulletproof setup stronger than a nine inch ford in many ways.

Works PB210 diff based on a modified 1600 Wagon in a similar fashion to the 180b Panel vans used for the Stanza works cars(Late US 510 and 160J or Violet in different markets.

Next was the JDM 180 B Panel van which was an oddball with 28 spline axles,This was a lighter housing than the utes and was the basis used for the Works Stanza Diffs with the addition of baffles and internal reinforcing tubes fitted to the axle section of the housing.Initially used with alloy centre diff housing metric 180B panel van type.
Later upgraded to 720 type cast steel centre due to bearing issues with big powered engines.
These works type diffs ran custom 28 splie axles with double width bearings,Basically two 240K type inner front tapered wheel bearing races in a single outer housing with a double width bearing retaining sleeve,Later disk brake falcons and a few others used a similar wheel bearing type,These resemble some of the cartridge type bearings used in front wheel drives and the front of later commodores.Advantage being zero pad knockback.

The works setup had a machined carrier that fitted into the bearing section of the housing,Used a smaller OD bearing and half the bearing width was retained in this adapter section outside the actual diff housing,They included the caliper mountings and all ran vented top hat type disks of 260mm diameter.They will fit inside some thirteen inch rims as well.

There is also some variants in the Nissan Vans that can be adapted in a similar fashion to the 620 and 720 Ute models with the six stud ute type diffs using a five inch PCD on the studs you machine the outer section of the axle away leaving a clean centre section to drill for new studs in the standard Nissan datsun four stud pattern,Far better than cut and weld conversions as the Metallurgy of the axles is unchanged.

Finally we come to the two Bluebird variants in the wagons series two with 25 spline axles,Series three upgraded to thirty spline axles.
Width as to be expected and normal wheel bearings.The setuo with normal wheel bearings allows the axle to move in and out giving pad knockback and a soft pedal with two or four piston type calipers,This is the reason these types use a single piston floating caliper as they to an extent compensate for pad knockback.

So when converting to rear disks you need to either use a fancy wheel bearing setup,Yte type adjustable endfloat axles or floating calipers to alleviate pad knockback for good brake action and feel,No point having rear disks especially on a rally car if you have to pump the pedal to get brakes working.

Well John has covered so many hypotheticals very well,I will bring to the table some more likely ones,Old often machined cylinder heads on most cars first thing I would check is that the head has been machined square and all the chambers measure up with close to even combustion chamber volumes.
Plenty of engines have been cooked in the past and someone just machines the head flat and bolts it on with a new gasket,Most bend up in the middle so when refaced end up with more being machined from the ends of the casting so the #1 and #4 cylinder chambers can be a lot higher compression than the centre cylinders.

Especially with an A series engine where pushrods and no cam tunnels like an OHC engine mean no warning sign of a Cam binding when you try turning it often means many now rather elderly A Series heads are best carefully checked or they will detonate on the end cylinders because of those problems.

First easy check for this problem is a straight edge along the Rocker Cover gasket surface,They were originally machined flat and square to the head gasket surface when they left the factory so a simple test like this will show any potential faults before they cause a problem with a built engine.

Mostly either Ring Gap as John pointed out or the above scenario as I have elabotated on are most often the cause of detonation caused Piston Damage or Seizure related stress failure's.

Try doing a google translate search on Yahoo japan for parts for a sunny Excellant,Not sure but South Africa also had some different stuff like that on some models over there,But basically the Sunny excellant range both PB110 and PB210 models were mainly Japan spec models,I remember looking for spares when the Ex Works Sheka Mehta PB 210 was in my posession years ago.Stuff is around and often in the strangest places.
Many early japanese vehicles seem to get manufactured in India as well these days,I own a Suzuki Mk1 GTI and that body shell is still in production in India as are very old 1950's vintage Austins called Hindustans.

Early 1960's Australian Ford Falcons were still being made in Argentina until 1992 so when looking for older car parts scour the world it may still be in production somewhere or at least made much later than you realise.

http://www.openaustralia.org/senate/?id=2012-08-22.114.2
This is a link I posted on another Forum I am on that shows just how long this Lying Government has actually been organising this Super Trawler to come out here to rape and Pillage.
This is a copy of the Hansard from the Senate which is the notes of what is being discussed and voted on so it shows who and what people are actually shafting Australians behind their backs,Hint the Greens are the Worst offenders who only want World Government and do not give a stuff about the Enviroment.
Condemned by their own words.

Earlier Volvo diffs are an option too as they used Dana diffs and Jeep components can then be used,Volvo axles were rated for use with steel snow paddles so they are tough as well.When you look at all the vehicles running Dana 30 diffs like the Volvos there are a good range of ratios available.
But when it is all said and done the Works Stanzas initially ran Alloy Centres but went back to Cast Steel housings due to reliability issues with the housing getting hot and bearings coming loose in the alloy with anything over 200HP motors.

In Australia there are two types of Stanza struts,Japanese Tokiko with a smaller stub axle and Australian made versions had 200B 240K Holden size wheel bearings with the appropriate bigger stub axle these are grey in color standard for easy ID.

That is a good grind for a full house Rally engine with something over 11>1 comp and a pair of twin sidedraught webers or dellorto or Solex carbs,way more than what you seem to intend the motor for use wise.

General rule of thumb for street use higher lift with shorter duration makes a good road cam as it retains good vacuum and pumping efficiency.
Cams with longer duration mean the piston is half way up the cylinder on the compression stroke before the inlet valve shuts and therefore feels sluggish to respond but revs out OK when it gets out of it's own way,That is why when you go to a bigger cam grind you need higher comp engines.
Most of the blocks and heads around these days have already been mmachined in the past so every one needs to be evaluated individually as to just how much they can be machined for optimum results,then add in is it a stock or stroker crank sauch as an A15 crank in a smaller engine or a big bore rebore as they all effect Compression ratio.

Just how high you can go depends on Ignition system Mixture quality (ie How good the Carb,Manifold and Exhaust work togrther) and just what we end up with fuel quality wise,For example in the past LPG conversions upped compression to make the same power as conventional petrol engines then the Government dropped the required octane rating of LPG available at the bowser and suddenly good working engines started having problems due to fuel quality being lowered.

Much to be aware of when planning an engine build for street use these days isn't there,but at least you are clued up enough to ask which helps get the good results.

Minimum would be 8CFM preferable would be 12~15CFM but make sure they are a belt drive with proper Pistons.

Many of the Chinese made compressors around rate on the Tank size rather than compressor flow rate,What I mean by proper pistons is that many of the Chinese cheapies have a conrod with a solid cast flat piston in one piece so at top dead centre it rocks from side to side as they do not use a piston pin assembly like a proper compressor or Car engine,the piston if fixed and part of the conrod and for rings they use an "O" ring.Total rubbish and only good for occassional pumping up of a slightly flat tyre.

When spraying panels a bigger tank can be more important than a bigger pump that supplies "Fast Air" and a quality second hand unit is better than a new one that is rubbish.
For quality finish a spray gun designed for metallic paints will give better results even with conventional standard non metallic paints as it has better atomisation and gives a smoother and finer finish off the gun.

As always preparation is 90% of a good quality good looking paint job and steer clear of anything IsoCyanate such as some Two Pack paint as Cyanide will either Kill you or make you very sick.

Old school acrylic paint allows easy repair of any mistakes unlike any two pack paints,but a combination of a good ACrylic color coat then getting a pro to apply the baked clear coat top coat saves you money and gives a modern tough finish if thats what you want,that is the system used by BMW,Basecoat,Acrylic Color coat then 2 Pack clearcoat for toughness on solid clor paintjobs.
HP w3ould be around 1.5 to 2 HP MOTOR
tANK SIZE AS ABOVE IDEALLY 12~15 Cu Ft
Air pressure depends on Gun type HVLP means High Volume Low Pressure and means generally a bigger compressor for that type of gun but an old school High Pressure or conventional Gun uses less volume of air but pressure vary from 30 Psi to 45Psi depending on paint type.THe HVLP uses between 8~15 Psi and has less "Overspray" but may want something between 15~30 CFM compressor with a much bigger Tank size for opotimal use.

Main thing you need it enough air to sucessfully paint your largest panel in one go which may mean 20 passes with the gun depending on panel size as you go left to right ,Up down and then both ways at 45 degree angle to ensure even coverage and good finish off the gun as that saves you much work later.

Firstly are you running an aftermarket ECu and what is it's abilities for resolution in ms.
When it comes to Injector sizing these days since the advent of the Bosch EV 14 Series and the modified versions available from such people as Injector Dynamics and Five0 Motorsport even a stock Honda Civic 1600 can run and idle with 1000cc Injectors,gone are the days of needing staged injectors such as used on the Ford Cosworth RS 500 Sierra.
Therefore when looking at injectors you can in many cases go for the size you are planning for future mods and use it on an earlier build spec engine sucessfully so only needing to buy one set of injectors for say a normally aspirated build that you plan to Turbo later.
These injectors will work very well with either engine spec so check out someone like Injector Dynamics for information,and when you actually talk to dyno operators with experience of them they will tell you just how nicely engines tune up on these injectors.
If you have never usewd them before I highly recommend checking them out as they really do work superbly.

i think if you search in the US you will find crank trigger setups,then you could look up Ignitec in Checkoslovakia from memory who started in Bike ignitions and have some very nice fully mappable ignition only systems that are very friendly price wise,so in fact are their full ECU systems,they have a very strong following over their in race circles.
Unfortunately people such as haltech no longer cater to the ignition only market,just a few in the EU,UK and USA still look after that market.
Best also if this thing is going to see any serious work not to run ignition of the cams as their is way too much timing scatter with belt drive cams when they drive ignition units,timing is not very accurate or consistent compared to crank trigger setups.

When all said and done it will take some effort to make up so you might as well do it right first time rather than have to spend the money twice to get the result you need.