If you notice, American cars from the 30's, 40's and 50's had aerodynamics built from the factory. Actually, some of these old cars get the same fuel mileage as the vehicles of similar size get today with 60 year old technology!
The Crosley was an astounding vehicle built from 1939-1952 and got 50 MPG!
More interesting info on the Crosley can be found
>>HERE<<