I've gotten low 20's MPG in a 318 powered 67 B body.
Those are light B bodies but not A body light.
Efficiency helps.
That was a 9.2:1 67 LA but it burned so well clean water dripped from the tailpipe.
The OP already has a more efficient ...basically everything, for sure heads and cam, which is more than half the battle.
...of course no way would that car do anywhere close to a 14 second 1/4.
