The Edelbrock #61659 Performer RPM CJ Bare cylinder heads are designed for use with 1968-87 429/460 Fords and SVO 514 engine applications. The Edelbrock #61659 Performer RPM heads are perfect for street performance, daily drivers, street rods and muscle cars where seat-of-the-pants performance is needed. These cylinder heads deliver great throttle response and power from 1500 to 6500 rpm. They also feature the highest quality intake and exhaust valves and valve springs. For use on pre-pollution controlled vehicles only.INSTALLATION NOTE: • Machined profile Cobra Jet-style intake port entries • Match with Edelbrock head gasket sets. • 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. • Recommended spark plugs are Champion RC12YC or equivalent 14mm x 3/4" reach with flat gasket seat. • Deck thickness: 5/8" • Rocker stud diameter: 7/16" • Pushrod diameter: 3/8" (width of slot in guide plate).