68 barracuda Exhaust Q

All right another silly exhaust question. I have the 340 HP manifolds I am using on my 340 Barracuda. It seems as far as head pipes (down pipes), there are way more 2.5 inch selection out there many more. Mine seem to measure inside diameter at 2 1/4. Is there some way to use the 2 1/2 pipes since there are so many choices? Thanks
Yeah, it's called bolting them on.