318 Maggie. When I bought my 92 D150 new it got 26MPG imperial (20 US). all stock 318 magnum, 518, 3.55 gears, no aerodynamics. So I think the smaller cubes in the light and slippery Challenger is the way to go, that and a Thermoquad carb, I'd keep the MSD but maybe keep a spare, known Mopar ECU from pick a part beside it. BTW, I've thought about a 273 Magnum as well, it could be a cool way to go, especially if you lighten the Challenger a bit.
