Small block mileage

My cars spend a reasonable amount of time on the Interstate. So they all get 2.71 or 2.76 rear gears. My 67 Dart is to nice to cut up for an overdrive, my 71 Polara in my avatar-well, it's just a cop car with a 440 and a 727, my 69 Coronet R/T will get 2.76's when I start driving it again. Anyone of these can run 85-90 all day long if I could get away with it.
get a gear vendor no cutting , works really well have mine for 8 years now helps big with the MPG on the highway 70mph+ . I drive 100 miles a day in summer at $5.00 a gallon back then and $8.00 a gallon now it might not have paid for itself but sure helps and car drives nice with no rev induced headaches . What I really want is an 8 speed from a smellcat , still waiting . for that I'd cut the floor roof amything