BB 440 Mileage?

I see that Holley Street Dominator as potentially robbing some gas mileage, especially since you seem to be going with stock 1976 pistons and heads (low, low, low compression) which won't work too well on the street with a single-plane intake. Put a good dual-plane on there (Performer RPM?) with some 3.55's and you should average 14-15 MPG. BTW I think you're severely underestimating the ability of a big-block A-body... Even with low compression, a somewhat small carb, and "only" 3.55:1 gears you should have NO problem getting into the 12's, of course only if the traction is there.