If the Magnum or LS valves are used with the 5/16" or 8mm stems and spring installed height of 1.8", beehive springs are readily available and valves like the hollow stem LS2 valves are light.
Back to Johnny Mac's original post and conditions, the intent is basically an improved stock replacement good up to 500HP. Porting and other performance parts in the aftermarket would vastly improve that, I expect. Keep the head valve train mass down. There are dual conical springs available now, but not Ebay priced. If using components designed for the General's LS engines, the parts costs come down.