I am dealing with the same thing on my 53. But, I have a 1963 C-20 that had a slide in on it all its life from California,(original black plates) and the bed boards and bed strips are a flat black and only painted on one side. Again no documentation. I had thought about staining the boards for my 1953 with an ebony stain, but I am probably going the route of a satin finish black paint.
Mike

My old truck's still running good, my ticker's ticking like they say it should, I got supper in the oven, a good woman's loving, and even my bad days aint that bad...Yeah, I'm a lucky man!
1953 Chevy 3100 Shortbed

1965 C-30 Panel Truck
1963 C-20 Long/Fleet Pick-up California Black Plate