The syncro's are pretty crap in the early turbo boxes.
Without LSD an MR2 still has considerably more traction than many other cars, so whilst it would obviously be better with the LSD, don't think it will be crap without.
It is this great traction that is the main reasons the gearboxes die. (or abuse)
I have often thought that if you had both boxes side by side, you could see if the lsd was interchangable, best way may be to start by seeing if aftermarket available lsd's share common part numbers, and if so try to swap yours. I really don't know how that would go though.