There are already about a dozen pages on a 318 mileage build up here. Search and I'm sure you can find it.

FWIW, my 3/4 ton truck knocks down 16-18 on the highway with a +.060 over 440, carb, auto trans, 4:10 gears, and 33" tall tires. Around town it drops to 10ish depending on driving habits. It is hard to keep your foot out a engine with as much torque as this thing has.