[William]

I agree with firstgenaddict. We did a '67 Z/28 years ago that was media blasted. I have several photos of the bare firewall with grease pencil stains all over it. "3L 2LG C08 Z-28 4L" are easily legible along with other markings that are not. The 2LG is partially obscured by the factory seam caulk. All of this was applied prior to any paint.

I have seen body color noted on the firewall after it was painted.

BTW the L89 in discussion was well known in the Milwaukee area when Pee Wee owned it. I sold him a VE3 bumper when the original was damaged.