The Edelbrock part # 77459 Big-Block Chevy Victor Jr. 24° 300cc cylinder heads feature an extra thick deck and extra material in the spring pockets for a heavy-duty casting that can be used with high-lift cam and heavy spring combinations. Edelbrock offers the complete 77459 cylinder heads with a spring packages to suit mechanical roller cams and 118cc combustion chambers. The 300cc rectangle ports produce impressive flow and great power on competition big-blocks up to 510 c.i.d. with 4.310" or larger bore. Exhaust port exits are raised .534" to greatly improve exhaust flow and power. INSTALLATION NOTE: Matching stud girdle #7797 must be used with stud mounted rocker arms. Deck thickness: 9/16", rocker stud diameter: 7/16", pushrod diameter: 3/8" (width of slot in guide plate).