so i'm rebuilding my original 1970 340

Oh my....Build and tune a stock 340 with 3.23 gears and stock 14 inch tires and save a ton of the money
...but you didn't want to hear that.
Except a stock 340 with 14" tires and 3.55s will not get 22mpg. It's going to take small gears (like 2.94 or less) plus an overdrive transmission to get 22mpg from a 340.