Maybe Jim has some ideas on this as I'll explain in a minute, but I'm claiming
on those. All drums are the same yet the red paint signified that Road Wheels were to be installed on the car. I highly doubt Chrysler had two sets of rear drums on the shelf since how would they know how many of each to have on hand? In theory, they could have 1000 sets of drums on hand extra each day and I'm pretty sure that's not good for business.
And with that, Jim has posted pictures of his survivor cars further back in this thread that not only show the correct style application of the paint but also shows the red paint sticking to the wheel after they were installed. Not flakes of dry paint, but wet paint.
So what I surmise is after the drivetrain was installed, it was noted on the line that "Road wheels" were optioned and they painted the drums. That would make more sense to me than a stack of red drums on the shelf. Too many logistical inaccuracies that I could list to have them painted by the supplier or by Chrysler when they arrived at the plant.
Cheers
Dave