To the OP, I had a '72 Satellite with a 225, and could get 22-24mpg on the freeway at 65mph. Its about the same weight as your Polara. This is with electronic ignition, clutch fan, 2 1/4" exhaust pipe to a Magnaflow muffler and a 2" tail pipe and carefull tuning of the 1920 Holley carburetor.