Tcodi's point about aerodynamics is a good one.

My 462" Buick powered 2400# Deuce highboy roadster gets 11-16 mpg.
Most times 11-12 mpg in combined town/highway driving.
The 16 mpg bit is on a long flat highway with virtually no stops and running the vacuum level as high as I can.

The 32 is about as aerodynamic as a brick.

The full size Buicks with similarly built engine - mild cam, single 4 bbl etc. - get the same mileage I do.