The Edelbrock #60579 Performer cylinder heads are designed for outstanding performance gains in 1962-79 389-455 c.i.d. Pontiac engines. The Edelbrock #60579 Performer cylinder heads are 50-state emissions legal for 1965-79 vehicles. 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. Performer heads are perfect for street performance, daily drivers, street rods and muscle cars where seat-of-the-pants performance is needed. They also feature the highest quality intake and exhaust valves and valve springs.INSTALLATION NOTE: • EQUIPPED WITH SPRINGS FOR USE IN HYDRAULIC FLAT TAPPET CAMSHAFT APPLICATIONS • These heads require Ram Air IV (round port) style exhaust manifolds or headers • Edelbrock head bolt kit #8549 • Deck thickness: 5/8" • Rocker stud diameter: 7/16" • Pushrod diameter: 5/16" (width of slot in guide plate).