You may have already gotten all the responses you were looking for. But i have a factory 69 M code and I have had 3 sets of headers. Hookers, Heddman, and no finally schumacher. I have to say the best $ ever spent. These headers fit great,easy install. They didnt need to be beat in to clear the torsion bars, or center link. The thick flanges are also a really nice thing. No more warping , I hope. Even though you have to use longer bolts now to install. Cant really comment on performance as my car will never see the track again. The car is worth to much, lol. But i have nothing but good things to say about the headers, and the support from schumacher. Top of the line.