426 dual guad. Gears go a long way to keeping the RPM down. Most of those cars came with 3.89 or lower gears so the RPM on the highway was hi.
I have a 1965 Galaxie 4dr with the 390 4V engine. Needs a valve job as one cylinder misses bad at idle, but still got 25MPG on the highway. One thing, those are imperial gallons, so US MPG would be about .8 of that so 20MPG US. Still when most of the muscle cars were getting 12MPG because of the gears. My Galaxie has 2.75 gears, so definately highway. I need to restore that cruiser.
