FRP 427 boss, I've run with Weber 48 IDA's and a Holley 750 Ultra HP. TKO 600 with the .62 od and 3.55 gears. I get 10 - 15 mpg with the Holley, less than 10 mpg with the Webers. (maybe cause I'm harder on the throttle with that combo).
Also have a BB 390 with Edelbrock carb, TCI C-6 automatic, don't know the rear ratio. get 15 - 20 mpg with that one.
No 1/4 times on either car.