no rpo sticker in glove box...or firewall...how else to get codes? need paint code

[PugDad]

Hey everybody, new to the forum. Just picked up a 1977 C10 Heavy Half step side last week. Nice truck, prior restoration started, very classy six footer.

Trying to move forward on some odds and ends.
I've looked in the recommended places for the rpo sticker/label/plate, but can't seem to locate it..glovebox, firewall, doorjamb....any ideas?

Other than going to the paint shop for a custom match, how do I find out the paint code now?It has a few areas that could use a little touch up.

I looked up the paints used that year, and it looks like the paint it should be is Firethorn Red...even though my truck looks less red and more brown.