Since you have a Mach I I guess you have removed the dealer undercoating and the factory sound deadener
Jan 69 cars are often found with the typical dark to very dark grey batch color where the base epoxy primer sealer was mixed with left over exterior color so the color was always changing a little (darker, lighter, more green, more blue......) Finish is pretty smooth and shinny
The final look can look pretty close to black until you compare a sample of true black against it as we've shown in some earlier examples from the same plant
Ass mentioned in many other threads this is for the firewall (approximately) rearward while the firewall forward was typically red oxide.
Though pictures shown on the internet do not always reflect their true look here are some pictures from a first week of Jan 69 San Jose built car