I'm confused. Do the 77 360 heads have the small exhaust port like a 318? You said there was a big differance between your 340 manifolds and the head's port. What are the numbers on your heads?
No Bob. The 340 & 360 have the same sized intake & exhaust ports which are larger than the 318's. The exhaust manifolds have a bigger port window. Why? I don't know.