I have a nice freshly rebuilt set of 3919840 square port heads without the thermostat boss dated E-18-7 & E-23-7. The heads have all new stainless valves and the springs will hold up to a 600 lift camshaft. These heads were used on 427-435HP tripower corvettes and 396-375HP Camaro and Chevelles for the model year. 330-770-2517 for any questions or pictures needed. $2500 for the set.