My car had been in a light front ender before I purchased it in '76, It had a replacement GM valence panel, spoiler in place, but the rods weren't there. I think it was common that the plastic spoilers were replaced without the rods in body shops, so I don't know how the originals were, but 'phosphated' would seem to match what Chevrolet did usually with such parts. An OTC NOS part may have gotten black paint, even if factory parts were phosphate only? Maybe a few folks with original unmolested unrestored cars with factory support rods in place can tell us what they have? and provide photos?