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I was smart enough to label this photo use_axle_38220-52F01.jpg, so I’m pretty sure that’s the U.S. axle stub part number I finally figured out. I can’t remember what the other two axles are in this shot. 
The mystery LSD (on the right) was from a car with 3-channel ABS. You can see the ABS sensor wire at the nose of the diff. The longer pinion shaft needed to accommodate this sensor required us to switch to a shorter driveshaft. Since a custom 1-piece aluminum driveshaft was probably in the cards anyway, that wasn’t a big deal. There's a driveshaft shop on just about every corner that can make a driveshaft to your dimensions.
The only markings we could find on the LSD itself were a little Hitachi symbol cast into part of it. Since Hitachi is the OE diff supplier, this seems to be a factory diff. Based on the super-short 4.38:1 final drive, I’m guessing it came from an early S13 powered by the relatively torqueless CA18DET. It’s equally possible that it came from some lesser 2WD R32 variant, of which there were many.
The diff uses 4 spider gears, making it quite strong. Hitachi open diffs often only have 2 spider gears, which makes them twice as easy to break.
If you’re not familiar with how 1-way, 1.5-way and 2-way clutch LSDs work, this is a 2-way diff. Torque from the ring gear turns the housing, while the wheels are attached to the spider gear shaft you see poking out between the two halves of the diff.
When you romp on the gas, the resistance from the tires causes the diff housing to ramp up on the spider gear shaft. As the halves of the diff get pushed out, they press the clutch stack together, locking the wheels together harder. This is a 2-way diff, since the ramp is the same in the on-throttle and engine braking directions. A 1.5-way diff would have a steeper ramp on the engine braking side, exerting less clamp load on the clutch packs so it has less of a tendency to go straight under engine braking. A 1-way diff has no ramp on the engine braking side at all. A 2-way diff is great if you have a car that’s too tail happy, like perhaps a tail-heavy 911. I’m more of a 1.5 or 1-way kind of guy for front-engine cars, since I like them to turn in without a fight.
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Trying to do this same GC coilover setup on my S13 with rear z32 knuckles for that OEM+ type ride all these years later. I have already had to step up from the original 7” 250lbs rear springs to 8” 250lbs which are still at the top of the threaded collar on the yellow KONI with not enough clearance between fender & tire. Currently about 1.8” of clearance between the rear fender & tire which still doesn’t seem close to the early pics of this project car. Do you recall if you had to use longer springs on the rear like I am (about to move up to the 9” 280lbs spring next in order to hopefully have a better range on the threaded collar)?