Oh, one more thing. Years ago I had a friend with an original 68 383/727 GTS. He lived in Sunnyvale, CA and was going to school in Northern Idaho. He threw a set of 2.76s in the 8-3/4 and fine tuned it and was getting about 22mpg on the highway. Top end was impressive, too.
I have heard of this type of mileage before from big blocks. You need a mello engine, basicly a stock unit with those gears and a reasonable tire size to do it.
