The Edelbrock #61599 Performer Pontiac Cylinder Heads utilize a D-Port exhaust port configuration for use with standard D-port exhaust systems. They are designed for 1962-79 389, 400, 421, 428 and 455 c.i.d. V8 Pontiac engines with a 4.060" or larger bore. They feature optimized oil return passages for increased oil flow. The spark plug has been relocated closer to the exhaust valve for improved performance. These heads are cast with extra thick port walls and a compact port size, making them ideal for CNC and hand porting. Complete cylinder head includes guide plates, rocker studs and high quality valvetrain for direct bolt-on application. Heat crossover is machined for 50-state emissions legal performance.INSTALLATION NOTE: • EQUIPPED WITH SPRINGS FOR USE IN HYDRAULIC FLAT TAPPET CAMSHAFT APPLICATIONS • Combustion Chamber: 72cc • 350 c.i.d. engines may require notching the block for valve clearance. • Three head bolt bosses are raised higher than the standard D-port heights and will require head bolt kit #8561 to install these heads. • Deck thickness: 5/8" • Rocker stud diameter: 7/16" • Pushrod diameter: 5/16" (width of slot in guide plate).