Good job
My '67 Mustang only get 6-8mpg
but it's not for commuting anymore...
Have you thought about some "vintage" like mods??? Possibly lowering it, a Trans-Am road racing style air dam or even a clear lexan grill block might help tremendously. I'm sure there are a lot of things you could do that can be hidden so no one knows, like a rear belly pan to smooth airflow out the back of the parachute like rear bumper valence. A more extreme approach would be going with an AODE trans to get a lock up torque converter, that by itself would help mpg quite a bit.