my 79 Bonnieville with 350 buick, egr blocked, second snorkle added to the air cleaner with cold air induction, no cat, big tube muffler, big tailpipe one size bigger primary needles, secondary rods on raised hanger, distributer recurve, magnecore wires, bigger coil on the HEI, .060 plug gap would get honest 21 MPG at 55, would get 12-15 pulling the bass boat depending on wind. Had to carry some instead of lead gold for when I got low octane gas, otherwise ran on regular.
Rod