As you get responses, keep in mind that horsepower measurement legally changed in 1972. So, you have to consider that your engine, which was rated at 220 hp in 1966, would be rated at about 170 hp today. That's where you are starting from.
Well, lessee If you max everything out with what is now available (headwork, cam, headers, distributor, carb), 1 hp per cubic inch is attainable. If you had a set of "soft" heads such as Endyn's, a specific cam, super high compression pistons to complete the package, you could expect 2 hp per cubic inch. 680 horses, anyone?
