I installed Dougs headers on my 69 convertible, had trouble because I needed bodymounts, and engine mounts. Once the mounts were replaced the headers lined up so good I could thread them in with my fingers. It was tough getting them there though, and it is close to the steering box. I also have the pypes system, and believe you problem is with the pypes system not the headers. I was incredibly disappointed with the pypes system and had problems from front to back. I actually had to have a shop cut me new tailpipes because no matter what i did(or the mufflershop did) they would not fit. Just my experience.
