I average 15-17 MPG with mixed driving and a decent amount of messing around (flooring it tee hee) in my '70 Duster. 5.9L Magnum short block with ported Edelbrock heads, 9:1 comp, custom-grind Racer Brown hyd roller cam, Hedman shorty headers into 2.5" duals, RPM (non-Air-Gap) intake, 750 cfm Street Demon carb, Mallory multi-spark CD box. 904 trans with cheap aftermarket converter that stalls around 2600 RPM and 8-3/4" rear with 2.94 gears.
I'm sure that will go down when I swap in 3.55 gears and a 750 double pumper but this car is transitioning from less street use to more track use, I have a truck to tow it longer distances now.
@doogievlg I didn't realize we were the same age lol I went to high school the same years you did