Bronze and steel gears for steel billet/roller camshafts and cast iron gears for the old cast camshafts. Now they have polymer gears!!!

This is the HD oil pump drive = M-6605-A427 390/427/428

There is no dist gear listing for FE engines in the '08 SVT Catalog.

This is from their write up, p 146:

"MATERIAL SELECTION NOTES:
Cast iron gears are compatible with cast iron camshafts (hydraulic or solid flat tappet type).
Steel gears are compatible with billet steel camshafts (hydraulic roller tappet type).
Bronze gears can be used with either cast iron or billet steel camshafts. They are usually
recommended by manufacturers of aftermarket billet steel solid roller tappet camshafts.
Since the bronze is softer than cast iron or steel, it will wear at a faster rate.
Polymer gears are compatible with all camshafts."