For what it's worth - the 1967 only, 1960-68, and 1965-72 Master Parts Catalogs, as well as the Standard and Utility Parts Catalogs, all show the Carrier (third member) nuts to housing as either Cadmium or Zinc Plated, and the Pinion Bearing Retainer Bolts as Plain Steel. The Washers for the Carrier Nuts are shown as Plain Steel in the 67 Only and the 1960-68 MPC's (3/8" nominal, 25/64 I.D., 21/32 O.D., 1/16 thick), but in the 1965-72 MPC (printed in May of 1975) they are shown as Copper, 3/8" nominal,13/32 I.D., 19/32 O.D.,3/64 thick.
Bob