Cheapest option would be keep whatever manifolds you have, keep the flange and 2" of pipe after the flange, weld 2.5" pipes over those that are bent to mate to a 2.5 to 3" merge Y, then a 3" high flow cat, single 3" pipe, 3" muffler of your choice and a 92-95 350 G20 3" tail pipe. Personally I would swap to headers or the Hooker manifolds. Summit actually sells a header/dual exhaust kit but they do not come with cats.
This seems like the way to go. I've been eyeing the Hooker manifolds for a while, as well as that header/dual exhaust kit, but this is a total pleasure cruiser not a hot rod so I'm trying to practice restraint and forget about the dual exhaust kit.
I've been doing a lot of reading but I still don't really understand this concept: if the manifold outlets are only 2.25" or 2.5", why would you want anything downstream to be bigger than that?
I understand that the extra volume would allow the gasses to expand and slow down, but I guess I don't understand why you would want or not want that, or
where in the exhaust chain you would want to modulate diameter.
Is the overall system not limited by its smallest diameter point?
Also, thanks for all the replies. I'll try and snap some pics next time I can get under the ole girl.
I will probably go ahead and replace the heat barrier on the doghouse when I do this, regardless of what I end up doing with the exhaust.