Mitch has a very good point about mataining exhaust velocity. Hank has a very good idea using the 292 manifold. If there is any way you could swing buying one I would recommend doing it. If its not possible at this time, I would get the 2 1/2 pipe anyway. The shop may have to weld a short piece of 2 1/4 to go to the manifold that you have.IMHO the 2.5 won't hurt a thing. My 78 integrated head nova has a stock 2 1/4 exhaust pipe all the way to the muffler, the first section is original. In 1979 Chevy came out with an upgraded 2bbl integrated head for trucks. The factory exhaust was split manifold with 2 2 inch pipes leading to a single 2.5 inch pipe then the cat, then a 2 1/2 pipe to the muffler then a 2 inch tail pipe. The exhaust was changed to go after more power. The cam and pistons were the same that you have. Now I wouldn't go to dual 2 1/2 pipes, that would fall on its face. Jay6155
