Frame from the firewall forward and the floor firewall rearward were typically rd oxide at that plant and year. Of course over that you have some sealers, body color overspray (heavier towards the outer edges and the pint weld black out over spray)
I looked through the pictures I have and I don't have a nice representation of that specific period. The firewall forward is typically a strong red oxide while during the 68 NJ production year the color can be a pale pinkish red oxide to a strong red oxide. Without pictures of another car from that period I can't offer any additional specific recommendation right now