Factory primer in 67?

Hey guys been a while since I've been on the site. Been pretty busy as of late but anyways, I started doing the body work on my 67 fb cuda. Car was repainted by previous owner some 30ish years ago , so I used aircraft stripper to get car down to metal to start fresh , I got down through most of the layers but now I'm down to this red layer which I'm guessing is a corrosion protectant of some sort or an etch possibly an etch??.. So it has factory paint coat , a primer coat ,Then this red coat which I don't know what it is and then that's on top of the bare metal.......

So my questions are ... What is this coating?? And since my car does not have any rust on it .... Is it ok to leave that red coat on the car and lay my epoxy primer over it ?... What I'm trying to do is save my self from sanding off if it can actually benefit me and provide more protection ...

I'll try to post a pic see if it comes up but you can see all the coats in this picture
The dark blue which last owner sprayed,then a primer under that , then the factory color which is a blue/sliver , then another primer coat , the red coat and then bare metal


Thank you all in advance sorry if it's a little confusing trying to describe best way possible