Its been found the valve train mass on the cam side does not matter much compared to valve side of rockers and valve control was more important than cam side mass, so the RGM steel kit is best way to go and diddle your Combat spot on by trial error creeping up on it, rather than trust some funny math, though that should put it closer right than factory Combats - which don't wear out valve train any more than spot on geometry but may valve float sooner.