the 604 your gs came with is very modable. As well as the neon tranny. There is several posts on the mods that are available, like final drive, kevlar, solnoids, stall convertors, tcm hacks, lsd, many many more. I have put around 2500 into my 604, Havent broken shit and I can beat the piss out of it. Even lay posi strips. :)