Performance mixed with fuel economy!?

Power and mpg are not mutually exclusive. The more efficient your motor, the more you get of both. First, what is up with the 360? Did you take compression readings? Not much difference between a 318 and 340 built the same. The manual 833 O/D is a good move and should work good with your gears, but can be expensive by the time you get everything. A Thermo Quad is the best carb, maybe a Holley Street Demon, TQ square bore copy, but I have not been able to play with one. Get your compression up to work with the gas you want to use. Get a cam close to a stock 340 cam. 20's mpg is within reach even with 3.23's - 2.76 without an O/D. Of course I'm talking highway cruising, not around town. Been there and done that, and loved it.