The USA '02 GT was NOT turbocharged. If you're intending to do a 'swap', there is a lot more to the process than just putting in a different engine. The wiring harness, exhaust, transmsisison, etc. all require major changes, too.
There are other Subaru forums that discuss the process. Search on NASIOC, etc.
But, yeah, DO NOT BUY a Used Subaru turbo engine.