318 MAX fuel economy builds?

I think that goal is reasonable and achievable. I had a clapped out dippy that got high teens and was a fender flapping refugee from the junkyard.

while all the generalities are of a concern (rear end gear, transmission operation, in good tune/running properly) I think that there is a whole other level that could be unlocked for little gains that may reap rewards not only in mileage but in reliability, a touch of performance and ease of operation.

little things like a sanden compressor for the AC, an electric fan, a denso alternator are all lighter and would free up power. lighter aftermarket rims free up horsepower, taller tires lower RPM.

a 2bbl vs a 4bbl would be an interesting experiment, as would 318 v 360. I'm of a mind that a well sorted 4bbl with tight 2ndaries would probably fare just as well as a 2bbl in the city if you kept your foot out of it.