go on youtube and look up clips of your year and engine car. thats what i did before i picked my exhaust.
IMO get a catted h-pipe and dual exhaust for a GT, it should fit. it sounds pretty good, and wil make you some power... not a lot. you don't have restrictive headers, so no sense getting new ones until you start building power.
however, if you really want to turn your car into something powerful, i'd stay away from exhaust. do a head/cam/intake upgrade first, and then you can do some LT headers and full exhaust.
__________________
|