For a significant performance gain in your 602 crate racing CT350 motor,Add these 135 lbs valve springs and retainers to your stock 062 and or 906 vortec heads! No machine work needed! Your stock 602 heads are 1.75 install height. My son is 4 time track champion and we put these valve springs immediately in all of our Brand New 602 motors.Your current valve springs are probably 85-100 and 221 lbs springs. This is a very effective trick! I also sell 1.6 stock appearing self aligning rockers sets separately in my store. I already removed the not needed dampeners.These are 30-50 pounds stronger in valves closed position and 100 pounds stronger in the valves open position. I also can give you more information on how to use these on a 604 crate racing motor.Feel free to message me with any additional questions or concerns.