for easy to install stuff, i would go with an ae86 LSD diff, should bolt straight into the ae85 mounts - someone else could confirm this though.
and I don't know if a t50 would bolt straight in with an ae86/t50 crossmember or not?
my 4age/t50/ae85 diff conversion into my ke35 corolla almost bolted straight in, just needed all the mounts moved slightly (except for the diff, but all the brake lines etc still mounted up the same) so I wouldn't imagine there would be much different between an ae85 and ae86 mounts.
but if you want to turbo it in the future to use for drifting, you could probably use a hilux or toyota crown LSD and a w55 box or something like that.
hope this makes sense
