myroc - As I mentioned before, even with supposed "bolt on" replacement parts, p to v clearance can be a problem. Almost every aluminum head or aftermarket cam out there is designed to simply "bolt on" the 5.0L - but that doesn't mean that all of them will go on without potential piston to valve interference issues. As you move forward, as mentioned before, anytime you add bigger valves than the reliefs were designed for or a cam that opens the intake valves sooner/closes the exhaust valves later, piston to valve clearance should be checked. Good luck with your changes.