/6 170 exhaust manifold swap

The '73 manifold will fit the '66. You'll probably need to drill out the center hole on the intake manifold to allow the stud on the '73 exhaust to pass through. Felpro makes a good quality set. It's the one I use. There are other good ones too but there are some crummy ones out there also. I recommend you DON'T mill the manifold in any way. It seems to throw things out of whack. Just make sure you have all of the correct fasteners, know where they go, and how they're mounted. It's a procedure that needs to be followed to lessen the likelyhood of crack and leak problems. Run a search for other threads on this subject. It's been dealt with in detail many times.