Driver for mileage

I'm pissed about the gas mileage from my 318 '70 Duster. All stock, 904, 2.76's in the back, it goes about a week back and forth from work (about 10 miles each way) on a full tank of gas, which equates to almost 12 mpg. I think it's from a multitude of things; stock points ignition, single exhaust, untunable 2bbl Carter BBD carb, and stupid low-rise single-plane intake (what were those engineers thinking???). Not to mention I'm driving at about 7000 ft. above sea level, and the car is originally from California. I'd feel better if it at least had some power too, but the only time it ever wants to go anywhere is from a dead stop!

I'm getting a '74 /6 Duster parts car, maybe I'll build up a nice turbo slant-6 and drop that in as the gas prices go higher (if I can't get my 318 to get at least 20 avg. MPG with upgrades).