Ah! Found it. The Model T was rated from 13 to 21mpg. That was a great improvement over previous cars, or at least that's what I've been told. Beetles (Type 1's) were rated between 26 and 34mpg. Not bad for a 1930's design! I've known a few who've got over 40mpg (HWY) out if them.
Back to the original topic, I don't see any evidence of single port heads actually increasing fuel mileage substantially. Actually, some of the dual ports got better mileage than some of the single ports. Oh well. I guess Ill go back to the drawing board.