I second L18B110 it is a modified L18 L16 1600 180B type sump,Stanzas and Bluebirds had the well at the front, The early cars at the back like that one.

Borg warner Boxes have that stupid screw in plastic gear change holder whereas Nissan Boxes use a Pin for the gear change lever to pivot in.

If you do a search on Youtube there is a series of six or seven Vids on the stripdown and rebuild of an Original one of these motors, well worth having a look at as rarely do you get to see how such an engine was designed and built.

Not if it is a standard .5mm or 1.0mm rebore but if it is a big bore you will have to check combustion chamber clearance around the edges depending on what chambers the engine uses not everything is as it left the factory some 40 odd years later in some cases.

Whenever you fix the bottom end make sure valves, Guides and seals are good or it will draw oil past the guides and smoke when you back off as the increased vacuum from a fresh bottom end will find problems that did not exist with low compression and worn bores.

Looks like the end flange of a H165 housing to me

Last Ute I built we used VW Passat Wagon Koni rear shocks worked a treat

Mixing and matching may work but what to be aware of is the number as the 63 in this instance means 63mm between centres of the two gearbox shafts.
therefore an A series has type 56 and 60 gearboxes datsun 1600 and 180B were 63 as is yours and the six cylinders and some later 4 cylinders FJ20 etc were 71 type boxes.
So the number being the spacing between the shafts gives you an idea of the dimensions of the geard, However while some interchanges can be made it is not always a given but is a starting point.

Type 63A 5 speed was 200B SSS, 180B SSS, Stanza(Violet) including GX and SSS as well as some homemarket models like some Laurels and Bluebirds.

Being a 120Y it can have either a borg warner diff (Plate on back) or a h150 in Australia as they came with either,The Lift out bolt in Diff centre H series is best.

If it is a borg warner then you will need a whole diff assembly and that means ideally a 1200 Ute complete diff,then you can find either a 3.9 or the more common 3.7 out of either a stanza (3.9) or Bluebird series one (3.7) and all of these are the stronger H165 and desireable for long term A 15 Power.

Why does everyone these days seem to think Billet is the go for everything.
Billet axles are the worst option for strength this side of Cut and weld.
All good axles are forged with no machining across the grain as happens with anything billet.

The only reason Billet anything is so popular is that CNC gear has become so cheap in the States and it is even cheaper to have made in China compared to Forged,It is all about the right material and most importantly the right grain structure in the metalurgy which basically means Billet is out and forged is in.

No Factory sports option stuff is anything but forged and that should tell you something,Billet is cheap to do to custom low volume applications and that is why they use it not because it is better.

Axles are the main safety aspect of many live axle conversions and that is the last place to cut corners,One does not want to look out the drivers window and see your rear wheel accelerate past the car.

L16 or L18 SSS heads were 219 casting number the A87 L18 head will likely have similar issues and that is corosion and you do not know where that may be.

L20B heads and V91 Bluebird heads while newer do need chambers welding up to bring the compression up.

For a road car I would go with a Stanza W53 casting and match port with the inlet manifold, the Valve sizes are no issue as likely any head will need Guides or K Lines and valves,So going up to A87 valve sizes really only applies to early L16 heads as 1971 on Datsun 1600's and Stanza's ran the 42mm inlet and 35 exhaust same as the A87 L18 heads.

Go for the newest casting with the right chambers which is basically a Stanza head and go from there would be my advice.
Anyone who for instance has a 219 SSS head will want big dollars and aside from the casting number and use with a full house Engine build with Webers etc is not needed in fact for a road engine match porting to a SSS manifold with a nice progressive taper to the valve makes better gas speed and a better engine with more flexability and no great loss of power up top anyway.

The best Road head I have done for an L series 1800 was in fact an early L16 with 40mm inlets and 33mm exhaust valves match ported to a SSS twin Hitachi manifold and the valve upgrade was only to 35mm late model exhaust valves,The Gas speed and response with the 40mm valves was superior as a road head to any 219 casting or modified A87 so proving those going to 280Z 44mm Inlets were going too big for anything under 2.2 litres

Inlet Port sizes were 38mm on the 219 casting,36mm on the L20B U67 and V91 castings and the W53 and A87 were closer to 31mm and when considering porting it is best to have a W53 where the process of porting is less likely to find water.

A good W53 will open up to 38mm to match the ,manifold and does not either need or want to be as big as a 219 casting further down the port.
Definately do not go for 44mm Inlets as they are definately way to big for an L18,Better to bore it to 87mm with 1mm OS 280ZX replacement pistons giving a capacity increase from 1770 to 1855 cc,Clutch wise the option datsun 2000 Sports replacment clutch will handle anything an L 18 with improvements can throw at it,They are still listed as there were the standard 2000 Sports clutch and the option with a heavier spring diaphragm which is still listed.