The Edelbrock #60139 Performer RPM cylinder head is designed as a bolt-on performance upgrade for any 1967-91 AMX Javelin or Jeep with a 343 360 390 or 401 AMC V8 engine. They include adjustable rocker studs and guide plates set-up for use with small-block Ford style adjustable 1.6:1 ratio rockers. The intake flange is dual-drilled to accommodate early and late model intake bolt patterns covering 1967-91. A Complete head includes larger than- stock valve springs to handle most high-lift cams. They feature stock location ports for compatibility with standard manifolds and headers. A direct bolt-on for 1970 and later engines with 1/2" head bolts This head includes step-dowel pins for pre-1970 engines. Their dual-quench combustion chambers produce approximately 9.5:1 compression in 401 V8 engines. The 45deg intake seat angle offers improved mid- to high-lift flow over the stock 30deg angle. The Edelbrock #601139 Performer RPM cylinder head has a machined heat crossover for 50-state emissions legal performance.