For mileage, my Chevy II got upper teens with a 3.73 gear and a 350 turbo. I didn't drive it long enough to really get the mileage up and a gear would have helped a lot or overdrive. I had a draw through on a 70 Nova with a 3.08 gear that got consistent low to mid 20's as a daily driver for years. It was a 4 speed and driving hard made it suck gas. I am redoing the Chevy II now probably with a 292. I haven't decided on fuel delivery yet but I would consider a blow through 2v on that engine too. Figure the air flow you need na and use that for the size you need for best driveability and the turbo will take care of the power. Use the power valve to richen the mixture under boost and leave the jets small for mileage. Holley uses the formula (RPM x CID)/3456 to get the needed cfm.
