I've done some research and have decided to go with the original 40's. I know go with the super flows with delta technology. bla bla bla.... I just like the sound of the original's better. willing to trade sound for the loss of the extra 1 HP gain. Anyway's I have been doing some searches and 2 1/2 inlet outlets have 4 dif part numbers. One enters from left side of muffler exits middle-Enters Left exits right- Enters middle exits middle and so on. Anyway's Just curious if someone had a receipt handy they could look up the Muffler #'s?? Maybe I'll just buy two the same and flip one over.