hey man a mate of mine had one of those engines fairly stock with a haltech in his gemini and it ripped shit for years, he did get it rebuilt at one point.. cost a fair bit but the engine went heaps hard, even with the stock turbo..
maybe u should keep the motor runnin for as long as u can, upgrade suspension etc, and then do a mild rebuild with more boost/larger turbo/intercooler?
just a suggestion, cos then u dont have to mess around with custom mounts for a different motor.. But if u really wanted to chuck out the single-cammer piazza motor and go unique u could try fit a CA18/SR20, 13Bt, or longer/heavier 6cyl 1GGT... RWD.. or 4A-GTE/3SGT but these motors are fwd and would cost lots$$$ to make fit..