Destroking an Engine

What is the objective? Fuel mileage in an A-Body?

318 with some sort of proper quench heads, quite mild cam which operates perfectly at the rpm range based on your driving speed vs. rpm, heat cross-over operational on a performer intake, small diameter tube headers, quadrajet or TQ, 4 speed OD with 3.23 rear end gears. Lighten the car where possible, lower it to reduce wind drag, run narrow tires to reduce rolling resistance, drive 20 foot behind a semi tractor trailer at all times.

What engine and trans and rear end gear ratio are you working with now?