how much of a 4th gen exhaust will fit on a 3rd gen? I know they say that LS1 headers cannot be used on a 3rd gen but will they fit with some small modifications? What about the Y pipe? Will that fit? How about the Catback? Are 3rd gen and 4th gen catbacks the same? I only ask because I'm leaning toward getting a 4th gen parts car and doing a LS1 swap in my 3rd gen. If the parts car has aftermarket exhaust, I'd like to use whatever I can to keep the swap as low budget as possible.

 

most of the intermediate pipe and the pipes rearward will work, the y-pipe is routed differently and wont work.
hangers may be a little different.

some fab and welding will be needed, but they can work

 

pretty much what he said. i had a stock 4thgen catback on my 82 trans am for some time before i sold it i had to make my own hangers for the rear and i had a 3.5in I pipe with a cutout that merged with the over the axle pipe from the 4thgen.

 

What about LS1 long tubes for a 4th gen? Will they fit with some modification?

 

No they won't fit

 

Just for emphasis - No.