Miles per gallon?

I owned only one slant six that got less than 20 in mixed driving with reasonable driving habits, and it was a new 1975, 225 Brougham fully loaded with options. It was in the15 mpg range. My current '64 Valiant convertible with a Super Six averages 17-18, with a high of 21.

The biggest problem today is government mandated fuel running in old technology cars. Ethanol supplemented fuel will drop your mileage a good 10%.