Actually, a set of standard-diameter Comp .500 lift springs or an equivalent spring that doesn't include the ridiculous Comp brand name price markup drops right in, and works well with that cam up to 6K+ RPM- - - -no need for special head machining. There's also a taper-wound "beehive" spring available that has a smaller diameter at the bottom and fits the original spring seat. You might have to shorten the tops of the valve guides a little to make sure the spring retainer doesn't get too close and mash the umbrella-style valve stem seals that work better than the OEM O-ring seals that fit underneath the split locks. If you use the umbrella seals, DON'T use the sheet metal caps on top of the springs or the O rings- - - -it's possible to seal the guides too much and wear them out. Eliminating the sheet metal caps also gives you a few thousandths more of lift capability before the springs try to stack solid. I use a piece of paper clip wire and a temporary solid lifter during assembly to check for coil bind- - - -if the spring coils pinch the wire, you're too close to a solid stack and need to machine the spring seat a little deeper.
Edit: There are several spring sets on Ebay that will accommodate a .500" valve lift, ranging in price form the mid-30's to just over a C-note. The springs that require head modifications are larger in diameter and will accommodate a second spring for sustained high-RPM operation like on a high-banked round track where the engine stays in the high RPM ranges most of the time. For the occasional tire-smoking session on the street, those springs aren't really necessary.
Jerry
