On a good day, downhill with a tailwind, a brand new 327 in 1962 might get 12-14 MPG. My father was the best carburetor man in several states around Nashville Tennessee, and that's the best he could do with them. I doubt if 50 years or so of use will improve that figure by much, no matter how expert your carburetor rebuilder or tuner is. The saying back then was "A 327 can pass anything but a gas station!"
Jerry
