Cadmium is a sacrificial plating. Its design is similar to a sacrificial anode. It protects the underlying steel by its own slow degradation.
After 70 years, cad plating on a hinge would be extremely thin, if present at all. It wouldn't take much to remove what is left of it.
I have an original hinge which has most of its cad plating on the underside of the bracket which mates to the cowl. It was preserved by the dumdum putty which was applied there originally to prevent water from entering the cab via the over-sized holes in the cowl there. It does not look at all like zinc plating, but is somewhat silvery in appearance. The rest of the hinge was raw rusty metal.
