The earliest year 427 I've got HP/torque info on is 1974. That year it was rated at 230 HP @ 4000 RPM, and 360 Ft/Lbs of torque @ 2000. They started dropping the numbers in 75, and by 81, some of them were down to 195 HP and 340 ft/lbs.
I'd suggest using the 4.88 gears and shifting at 3500-3800 RPM, wherever the shift puts you at or neat the torque peak in the next higher gear. Obviously, you'll need to do some tinkering with the governor to get it to wind up that much.
Jerry
