I don't see any evidence on my car of red oxide primer, and it's definitely a dark, dark blue/gray almost black color from the firewall back. 100% positive and that's how I'll repaint that detail.
Now, concerning the front frame rails I do have a few questions. Let me see if I am understanding this correctly.....if you were to take a profile shot of the car and extend the line from the vertical portion of the firewall straight down onto the front frame rails, that is where the red oxide up front would start. But wouldn't this be all covered in black when the engine bay was painted? Or are the undersides of the front frame rails, front strut rod mounting rails, not painted black and they'll show the red oxide underneath? This is how it's done on my Bee, but the underside was a dip gray primer. The car was painted with two painters walking the car and when they sprayed the engine bay it was from the top down. So where they couldn't reach it remained gray: under side of the frame rails, battery tray, firewall lip, etc. Would this be the same detail on my 68 Mustang? From the top view down inside the bay, black. But looking upwards from the bottom, the underside of the rails, strut rod mounts, front core support, etc would all be red oxide....specifically on my 68?
I'm well versed in the Dodge realm of things, but not the Mustangs yet, so I'm scouring for info. Understanding the paint process aids the understanding of what was painted what color and why. It's interesting for sure!