Dave,
What a wealth of information your dad could be to this board! Anyway, I agree most, if not all, were black. My thought is that like the sway bars & leaf springs, the boxes had an oily film on them that caused the paint to come off very prematurely-leading to the misconception they were bare metal. Having said that, I will never say never to a Mopar. I'm sure some got through without paint by a lazy employee.