I tried the Pypes down pipes that they advertised would fit our FGFs. Because I live in CA they could not ship them to me here. Had them shipped to a buddy out of state and picked them up from him. After all that I found that they did not fit correctly onto the factory manifold. The 2 1/2” flange is too wide to fit our manifolds. The 2 bolt flange bracket did not even fit their flange correctly and wasn’t even round. There was no way they could install and not leak. At least I could return them from CA. My solution was to make my own flange from 2 1/4” pipe only about 1 1/2” long and weld them to the 2 1/2” down tubes that I also had made by following the bends of an original 2” Firebird pipe. They came out perfectly.