The Edelbrock #60569 Performer cylinder heads are designed for outstanding performance gains in 1962-79 389-455 c.i.d. Pontiac engines. They feature 87cc combustion chambers designed to maximize performance while using less expensive, low-octane fuel with a streetable 9.5:1 compression ratio. They are patterned after the 1969-70 Ram Air IV Pontiac cylinder head.INSTALLATION NOTE: • Bare heads will have valve guides and seats installed, but will require final sizing and a valve job to match the valves you will be using. • These heads require Ram Air IV (round port) style exhaust manifolds or headers • Edelbrock head bolt kit #8549 • Deck thickness: 5/8" • Pushrod diameter: 5/16" (width of slot in guide plate).