Best replacement would be to try and find a stock turbo for it. Next step up would be a TA49, which is a great turbo, but requires fuel mods to keep up with it. What does the car have done already?
The Ta-33 is the only thing out there that will bolt right up. other turbos you will have to moded and make sure they have the proper internals. this subject has been covered. try a search in the hotair section there is alot of reading to be had.