I have Doug's on a 67 400 auto coupe. They fit great with the exception of being a bit too close to the floor boards on the driver's side. I had to put a very small dimple in the floor to allow for clearance for the top of the collector flange.

I also thought the width of the Pypes system is adjustable out from the front of the X-pipe as those pipes come forward at an angle and the lengths determine the width at the headers. I have the instructions here with me as I am getting ready to have my Pypes system installed soon.