i think the reason why he wants to swap the turbo's, is because the one he has is on its way out. i think it needs a bit of work done to get it running perfect again, and i think that instead of doing that he was looking at buying a t28 which can also be hi flowed a lot to make 250kw atw.
what are the specs on the standard 1990 gt4 turbo?
is it BB? what hp is it?