Potential yes for sure, gas mileage yawn ya I guess, longevity for sure but all engines ran forever back then. Good fuel, oil, and work pride did that. But man were they dogs. I would hate to put up the number of times I beat 318 A bodies with my six cylinder ford maverick. (I was almost a Furd guy) I only owned one in a 318 (1976) Dodge van and I gave it to my neighbor when I built a 360 to replace it.
Well, imagine this. We had a friend in school who had a 64 or 65 Falcon....I think it was a 64. 2 door post. We helped him pull the original 170 out and put a 300 in it. It would wear out recaps on the back within a week.