Hi Elliot
I have an R31 LSD in my 1200 ute that I race on a regular basis. They are actually quite strong and also cheap to rebuild. I have been told by several people that the cones are still available new from Nissan for $90.
I know of an RX7 drag car that does 1.3 second 60 foot times that is still using the same diff as mine and has never needed a rebuild.
Have you thought about buying a wrecked or cheap R31 Silhouette, pilfering the diff and then selling off the panels, motor, alloys etc? You will probably come out ahead dollars wise.
Regards Matty