It has to do with the metal used on aftermarket roller cams. They are usually made from a steel billet vs cast iron for your typical flat tappet cam. The steel being harder than the cast, so a bronze gear is required. I am not 100% sure but I think the stock magnum cam can use a regular gear. I bought a magnum billet cam from hughes, but they had put a cast iron gear on the camshaft so a regular gear worked.
