First, my apologies if this is a newbie question. We all start somewhere.

One of the previous owners of my GTA had an aftercat system put on. It looks stock from the manifolds to the cat, and after the cat it's what looks like 3" stainless all the way to the muffler, with two 2" or 2 1/2" pipes from there. There's a couple of numbers stamped on the muffler but nothing to identify it. Is there any way to tell what I have, aside from tracking down the previous owners? Anything to look for? When the cat eventually rots out I'd like to get headers, a y-pipe, and a new cat to match what I already have (the little 305 sounds great). Thanks.