The way to go:
Ford 9" Narrowed with perches for your springs.Adapt the rear of your drive shaft to the 9" yoke . If drag racing only and you trailer the car get the pro style gears that can stand the shock abuse and a spool.
You can get after market gearsets,carriers , axles &housinings & brake kits for the Ford 9" anywhere in the U.S. and many other places 24/7 via internet or phone and have them waiting at your door in a matter of days.

A Ford 8" would be a second choice but the performance parts & axles for those are not as plentiful. The 8" were available all the way from the early1960s up to the late '70s on V8 Mustangs, Mustang II(V8-V6), Falcon , Comet , Maverick,Fairlane V-8 cars.
The 8" is not reproduced so what is out there is either stashed cores inservice stuff or older wrecking yard stock that is rapidly disappearing around here in Southern California.
Some of the later model Nissan & Toyota stuff is good too and there are aftermarket parts for race applications available.
Later model Nissan differentials seem to have a problem with aftermarket performance parts availability though.
When Nissan pulled the plug on Nismo they pulled it hard.The baby went out the window with the bathwater.The old catalogs are wishbooks for collectors now.

I've broken 2 Datsun H-190 differentials racing on them using 4.88 gears ,8" slicks and a strong L-20B 3800 to 4000rpm launch on a good hooking track.
The stock side gears are not up to the repeated stresses nor is the side gear cross shaft and it's retaining pin. Seperate failures on two different occaisions.When the cross shaft walked out it was almost catastrophic failure at speed.Tore the teeth off about 1/4 of the pinion gear.Not pretty.
Forget finding an old Nissmo posi unit , locker or spool unless you know someone who knows some one that has a pile of that old stuff stashed somewhere and is not pricing it like it is made of unobtanium.
Welding up the side gears to make a "Lincoln Locker" out of it must be done expertlly and then the whole unit must be completely cleaned and re-heat treated / stress relieved for it to be even near safe to use with confidence going down a race track
There are no new High Quality Race only gearsets being made for the old Datsun diffs any more.
The NOS parts for the old Datsun diffs are drying up and they are getting harder to find at the wreckers.
My experience now teaches me the old Diffs are not worth the trouble anymore to try go racing on, reliably.
The old stock gearsets still are not up to the repeated starting line launch hits ,especially in a good hooking car.

The added weight of the Ford Diff will help the tires bite better .
If you are worried about the extra weight
lighten up the car and make more power 'cause now it will handle it.

Sprint250 - if I could hijack the thread for a second - out of curiousity - what sort of power/torque does your l20b put out, and how heavy is the car (and what times was it running when it started breaking h190s)???

I don't have datsun specific info on this, but when I upgraded a torana diff from a stock holden banjo (which are notoriously weak) to a ford 9" (for a turbocharged 202 ci pushrod 6 - like a baby brother to the chevy inline 6 with siamese intake ports) - aside from no more worrying about breaking bits, I definitely noticed the car was a lot more stable, consistent, predictable (and hence quicker) off the line. The extra weight in this case was actually a bonus, and no doubt the axle tubes themselves, being larger diameter (and at least the same wall thickness) made for a more rigid setup.

Although the car did have decent output, even when the motor was non turbocharged (basically when the motor needed work I'd throw in an NA mild motor to keep the car on the road/usable) the usual rumours of a massive power loss due to the heavier diff/axles - well all I can say is it's usually blown out of proportion.

The 9" has an advantage over the borgwarner 78 (which is essentially what is in the vl commodores, various models of ford, skylines etc in Australia) - aside from strength, is the removable centre. It leaves the option of a locked/spooled diff for the track and an open or lsd diff (possibly a different ratio too for better economy and lower highway rpms) for a-b stuff. With teh borgwarner, you have to setup the gears in the complete housing, so you can't exactly change ratios/centres quickly at all.

most of the bw diffs were 25 spline, but more recently they are mostly 28 spline. a quick tid bit - and I found this out by surprise (as it turns out a local diff shortening/adapting/fitting shop does this so they can save on costs - they just use second hand axles from the wreckers as is) - anyhoo the 28 spline bw axles will fit into ford 9" side gears apparently.

umm going in a different direction to a ford 9" i rekkon you should try and get the lightest diff you can. maybe get a custom spool made up for a slightly larger diff and spline it for bigger axles out of another car or billet axles? or if you really wanna splash out get a winters quick change, rated to 500hp, weigh about 45kg and you can change ratios in 2 minutes without lifting the car off the ground.
a heavy diff can completely transform the handling of car in a bad way. my torana diff pushes mine around and i can feel it making the car understeer. if it's only a drag car not designed to go around corners a big heavy diff should be alright but will still rob power.

unless your making a massive amount of power a 9" is NOT the go. they suck a heap of power and are very very heavy. if your planning on running 9 sec or quicker w/ a rotor then it might be the right choice

any more info on shortening a hi lux axle by using two short side axle tubes? this sounds like a cheap and easy way of getting a strong axle that will fit.

Jmac
This thing is still a driver and was meant to be primarily something we could take to the track and beat on all day long and then drive home in.
The 69 521 truck weighs 2450 lbs. wet w/ driver.
The L20B is making maybe 120/130 at the crank on a good day.
The 4.88 alloy carrier was open non posi but by careful ballasting I was able to get both tires to grab... sort of.
I am not nice to this thing .I have tried to slip the clucth but it just slowed .Best reults were revving to launch rpm and side stepping it.
Battery is in the back.
2" lowering blocks in back and torsion bars adjusted up to help weight transfer.
Also using a pinion snubber over the diff.
Pinion angle is set 2 degrees negative
Screaming to redline in 3rd across the stripe.
Best 1/8 mi et to date is 10.62 (super slow)at about 62mph.And the 60' times are terrible.There is a lot to be gained there.
If I can knock .5 off the 60'
I will be a happy man.

We are however consistent and have won some bracket races with this rig.
Faster cars hate me. We have surprised a few so called hot or muscle cars in heads up races.
I'm currently using a 22 .5" dia. MT ET Drag mounted on 15" 6 lug Chevy truck rims.
We tried to use a 10.5 MT ET Street slick but it only lasted 3 passes and broke the spider gears on#4 right at the hit.
We patched it back up and went back to the shorter tires and ran our best times

So far money has been the limiting factor here and my goal was to use this as a test bed for chassis tuning but busted third member sets were sidelining me too much.
I'll take the extra weight penalty of the nine and make more power.
The H190 gearing is laid out similar to the 9" so the power loss is in the weight and once the 9 is narrowed probably not as big a weight penalty as initially percieved.
I'll post back when I get the nine put in it.
It is back on the road this spring.

We also race a 65 V8 Ford Ranchero that uses a stock 8" rear and it has never failed....yet.
That car is heavier makes about 330 horse and is way faster than the 521.

The GM salibury type rears I do not like because GM chose to use the axle surface for the inner race of the axle bearing. this eventually destroys the axle surface that the bearing rides on making it junk.That coupled with the fact that the the GM 10 and 12 bolt diffs use C clip axles and you cannot easily swap gearsets/carriers keeps me leaning towards the Ford or other Hotchkiss style differentials.
On a side note while in a wrecking yard looking for H190 gears I measured up an 88 Path Finder and the whole 4 link rear end assembly w/ coils looks like a close fit in an old 521 truck. It would take som fabrication skills to do it but it looks possible.

bastard hilux has EQUAL lenth axles. how inconsiderate mr toyota.
i have heard if you use late camry wheels you can get away without shortening and they are the same 5 stud pattern

when i was talking to lags about the hilux diff he had in the wagon, which is now in anges ute. he said that it was using shortened 9 inch axles, which i figure is because you cant cut down both hilux axles and end up with the stock 1200 width

so you either have to only cut down one axle and have the centre off to one side, or use other large axles and have them cut down and resplined to suit the hilux centre