What size header bolts for a 72 340?
Ditto on denting the primary tubes. The only one I needed to was the #7 (rear driver's side) but I could tell I needed to before I installed them. I had a hard time putting a bolt in that hole when I tested it ahead of time. I'd suggest trying to scope the headers out closely BEFORE you're fighting them in the engine bay. I had a spare motor sitting that I test fit mine on but you don't even have to have another engine to test your wrenches for reach.