i have a 383 stroker 9.5:1 pistons cam is .480/.480- 230/230- 107 spec it has 76cc cast heads, comp springs .530 lift and 2.0 valves. the problem is i got the motor running dialed the timing in and drove it. 100 miles later #6 cylinder broke the exhuast rocker and bent the intake push rod. it has stock rockers. i put a new rocker and pushrod on and it was fine until another 100 miles #8 cyclinder broke exhaust stud and broke pushrod on intake valve. the builder of the motor says it is getting to hot in the cumbustion chamber and causing the valves to stick. both times it broke it was not running hard at all. i was told roller rockers will solve the problem. any suggestions of whats causing this?