I agree with Caddyman about the timing and the carburetor power valve. The latter is a common problem on aged Ford carburetors anyway.
Also in agreement that this truck is never going to be a mileage getter even if everything is spot on.
Many years ago I used to own a Plymouth Roadrunner and a Dodge SuperBee and if driven gently I’d get about 8-10 in town; and by gently I mean driving like there was an egg under the pedal. “Normal” driving would drop it to about 7 and a heavier foot would put it in the 5-6 range. Watching the gas gauge plummet before your eyes hurt a bit but it was fun to do at times.