As mentioned in a number of other threads it appears that originally they were a dark heat treated steel like other parts such as spindles, some of the steering, and rear leaf springs. In some limited cases (not sure if this includes the 71-73 - haven't seen that) some were painted a semi-gloss black. Service replacements were painted black also so that adds to some confusion with some of the findings
Most will strip and refinish the surface as needed - then stain the metal followed by a protective coating of protective oil. This last step follows adding/replacing any paint markings that would need to be replaced
Might want to look at the article in the Library titled Natural Finishes- Reproducing