I didn't think 16 mpg sounded to bad for a '48. It's not fuel injected, has a standard ignition, and is probably not very aerodynamic. Not to mention, that it is a pretty heavy vehicle.
It's a fact that burning a little rich could definitely affect the mileage, but I still think that 16 isn't bad.
I would never dream of 20 mpg or better, am I way off on this one?