Just reporting back on the D660YA headers. I built a 331 from my 289, I rebuild the C4, new servo and transgo shift kit. Decided to install the engine and tranny together the same way I removed them. installed the starter, battery leads, engine mounts and oil cooler lines so I wouldn't have much to do under the car.
I decided to install the passenger side header before lowering the whole assembly in figuring I couldn't do both headers, this was a terrible idea lol. Between the engine mounts and oil filter it was alot of extra work! I had to saw off the end of the upper control arm studs. I couldn't pull the oil filter because I put fluids in the engine which was another terrible idea! I also sawed of a little plug of aluminum off the C4 bellhousing on the driver side.
Overall the headers fit great and I didn't have to hammer them anywhere! I am sure lowering the engine into near final position FIRST then installing the headers and lowering everything would have been best!
For the rest of the exhaust I bought:
stainless flanges HVF10S
stainless X pipe kit PN: XVF10S
Borla ProXS Mufflers 40659
Bought these over axle pipes for a mustang from ebay, they are currently 3 inches inside the rear bumper:
Stainless 2.5" Dual Exhaust Builder Tailipes 65-73 Ford Mustang & Mercury Cougar