Ive checked here and there, and there is no definitive answer to what headers / manifolds work on a 351. I dont know if anybody here remembers me or my car, but i finally got a windsor and its time to squeeze it in there. (thats what she said jokes aside)
Crites. 1 3/4 individual tubes. No dings required. They give a pattern to cut out part of the shock tower and the metal pieces you need to weld in ... but you might as well do the full shock tower shave.
I have literally nothing but the frame rails. If I went to go for a 351 would I have MANY MANY options? or is it a notch have to be in the frame?
The worst fitment problem with a 351W in a Mav/Comet is that the front two exhaust ports point straight out at the shock tower where the upper A-arms are. The second worst spot, pretty much with all headers, even for 302s is a lot of them tend to be close to the inboard limit of travel for the pitman arm. A floor shifter (if you have an automatic) is likely to be needed too. The headers for my swap, that was done in 1996, is used set of unknown brand (we suspect BlackJack ... got them from a friend). An inch was removed from each tube to narrow them, and they are far from optimal... two tubes leave the ports at a tight angle.