Yes, red oxide or black is most typical. If I didn't know how a car came, I'd be searching out cars close in production at the same plant to get an idea of what was being used at that time period. You can get by with either one from an authenticity perspective, black/grayish-black might have been more common though. Also, consider that there would be several stations where primer was sprayed, so there can be different colors on one car. We've discussed this at length in the past, probably some good info to be found using search.