318 and 360 gas milage question

I had a 360 give me 20 mpg's with a upgraded in power with these parts;

Carter 625 AFB on a factory iron intake and a K&N filter inside a '73 , 340 air cleaner.
MSD -6A, viscous fan, dual exhaust off the manifolds @ 2-1/4 with a "H" pipe.

A 904 backed it up and a 8-1/4 rear with 2.76 gears and 235/60/15 (approx. 26 inchs) all around.

The car? A '79 Dodge Magnum. A Cordoba based unit @ 3650 lbs.

For certain, you can do the same in a lighter car and possibly afford a gear change. I would yeild at 3.23's.
More mileage can be found with headers (Coated if possible to reduce heat in the engine compartment.) and a X pipe, a better intake, manual trans for it is a direct drive without converter slipage. Tire size has a small impact on mileage. Smaller items I did not consider useing them would be minimal in mileage gains, but could show something. Like an electric water pump, manual steering, no A/C, skinnier tires, taller tires (are good for the Hwy.) A cooler for the oil, tranny fluids.

On a carb size, if mileage was the goal, a 600 cfm or less carb could still power the engine well. Just do not go changing cams and upping the compression ratio and etc.......
A T-Q carb, if tuneable or a Quadrajet could possibly show some gains while having the abilty for big cfm on wide open throttle.