You are one of the posters that asks "What Plant?" or "What year?" on detail questions like this, so, I'll do the same.
What I've seen are rusty or oil covered bolt heads, rusty or covered toothed washers and shiny threads on brake cylinder several 65 and 66 San Jose cars that I own or have worked on, eg zinc. I also note that the two piece Ford Service replacements (screw and lockwasher) are zinc (cad) plated. Were phosphated screws used? Sure. Ford's prime concern was making and selling cars, not documenting what they did, so a line replacement could be anything to keep the line movong. Keep this in mind, the brake cylinder was attached to the backing plate as a sub-assembly along with all the other brake related parts. I assume it was under Ford control for assembly as well as quality and these parts were specified for service based on the original factory spec, although we know that to be misleading.
Jim