the difference in compression ratios were different chambers and 2bbl vs 4bbl pistons. using stock hydraulic cam valvetrains may be the biggest culprits to piston to valve collision. when the springs would float the tappets would pump up (keep in mind .100+" pre-load on the tappets) and the intake valve is into the piston. tight lobe separations, added duration, aggressive lobes, increased lift just makes matters worse. keep in mind that the intake valve is chasing the piston on it's downward motion and the valve is moving faster than the piston. valve reliefs are the only true answer to the problem. a stock magnum cam with slower ramps and wider lobe separation is safer but like all hydraulics needs pre-load reduced. aftermarket rockers usually have higher than advertised ratios so using them may not be the cure.

the 2315's are easy to use but can set you up for piston to valve collision when revving the engine up. the kb162 is safer and lighter. another thing; big valves will give you a little less piston to valve clearance. advancing the cam will reduce clearance, AND, don't over cam a 383.