Slant 6 most mpg's

just picked a 76 dart lite 4 speed, i want to squeeze the most mpg's pout of it.
going to have the engine rebuilt, should i make any modes as far as pistons, cam,etc..?
1bbl or 2bbl? if i go with a header would that affect back pressure?

What's your end goal for maximizing MPG?
If its "saving" money, then NOT spending on parts is worth a LOT in terms of imagined mpg "savings". Even NOT spending $50 is worth quite a few mpgs.

If it's just for fun in general, what is the budget?
Fuel injection running a lean 15.5:1 A/F closed loop during cruise and computer controlled timing, would be the way to go.