I got an H-pipe for my 70 Hemi Charger from Don's. I was happy that it looked correct, but when I went to fit it the pipes were way off at the tail and would have rubbed the driveshaft. Since both R & L were to the same side I was left with no choice but to saw off a 3/16s at the manifold flange, reflange it again and HOPE I guessed right. You don't have much room for error on this. Luckily it fit after the first try. I had to do this same procedure 20 years ago with an H-pipe on a Hemi Cuda. If I had to do it all again I would tell them to NOT weld in the crossover pipe and ship it loose. Once that crossover is welded in place your ability to tweak ANYTHING is LIMITED.