The problem is a stock magnum head will have 8mm dia.valve stems so the keepers will have to match the retainers. I went through this a while back and wished I had not used a magnum head. Huges was the only place at that time that had a complete HP spring kit that dropped right in with no machining of the heads.Even Mopar did not have a "drop"in HP valve spring for the Magnum head.