Well, first off, it's not as bad as it sounds. The carmakers changed the way they reported flywheel horsepower in the early 70's by running all accessories on the motor, whereas before that time they had run the motors less accessories.

There was a real problem with these motors though, and that was the lack of static compression ratio. the arab oil embargo was in full swing and the tree huggers were screaming about cleaning up the air, so we were all forced to change to unleaded, low octane fuel.

These motors need to be torn down and the squish needs to be tightened up as well as the static compression ratio increased. Also, my friend Ken Thomas tells me that the timing marks on the timing chain sprockets were retarded, so you would want to use a '68-'70 427/454 timing chain set.