I am pretty sure bumper brackets were dipped in black paint hanging by a wire. I have a lot of brackets taken from western cars years ago. There is no primer, found lots of runs in paint.
Thanks, Bull1tt. Good info. I'll remove the mill scale, fill the rust pits, and dip paint.
FWIW, almost every black part made in-house by Chrysler (there were many dozens) on my '69 Barracuda was dip painted with runs. Mostly only the rear axle housing and the K frame were spray painted black. Exceptions are parts made elsewhere, such as the coil and A/C parts.
