I do not conclude the pick-up box tail-gate/end-gate cable came zinc/cad/galvanized, nor do I disagree about a black finish (which I would prefer). "I think the original were zinc/galvanized plate", but I would not bet (or disagree with anyone) on any possibility.
Also, my experience is only with 1954 - the pick-up box end-gate/tail-gate chain assembly changed that year. I have no doubt that a cover was available in 1954 (and, I assume that a cover was available/used in earlier years, but I cannot find documentation for that).
