Im keeping my stock exhaust manifolds on my 307 but im putting dual exhaust on. I found 2 1/2'' downpipes from Pypes and i was going to order a 2 1/4'' header back exhaust from summit. Will the 2 1/2'' downpipes mate with the 2 1/4'' exhaust kit? Will the 2 1/2'' downpipes connect properly with the stock manifolds also?