what combo = decent mileage+ power/torque

My first hot rod dart had a 318 with 360 heads (8.5:1 CR), headers, a TQ, weiand dual plane intake, fast recurved electronic ignition, a crane econo power HMV 278 cam, 4 spd, 323 gears and short 24 or 25 inch tall tires, it regularly pulled 17-18 mpg on the highway, and ran like a raped ape.

If I were you I'd consider picking up a remanned 360 on the cheap and throw some hot rod parts in it. Cam, timing chain, valve springs, lifters. Look in ebag for a deal !