dc sports does make one for the gt. supposedly they make better power than the hotshots, but i havnt seen dynos to compare them yet. both companies are fine, although i still prefer dc sports.
the installation is bolt-on..but its not simple. i'd say more difficult than CAI
or exhaust, but much easier than turbo (which unless you are a mechanic you should not do).
i looked for an install guide but all they have is for the amss headers for the gts. you might want to check it out anyway though..it should be at least similar.
and if you're not certain..you can always go to an autoshop, ableit for a price.