http://winnipeg.kijiji.ca/c-cars-vehicles-auto-parts-tires-engine-engine-parts-1975-Pontiac-HO-455-For-Sale-W0QQAdIdZ273959855
These heads have umongously huge chambers ie. 124cc... not too high output ! Myself I would replaced them with 6Xs off a 1975-79 Pontiac 350.