You can pickup a diff for cheap at most scrap yards from a supra... It has to be a non turbo diff if I remember correctly. Have a look on Escos.com or speak to MK Motorsport (I think it was them) They have made the kit and sale the diffs with it. The dif is cheap as chips at a couple hundred.. or they was at least.

Apparently builet proof.... but you then have to start upgrading other parts as they then become the weak part of the system. The diff it had in there took anything I threw at it and the two previous owners to that. The engine, diff, gearbox and beam etc all came from the same car which was known by the guy who built it. He sold his ST 200 block engine and replaced with that one, had it mapped and off he went.

That car would spin happily in third gear in the dry