Wow, I am learning something here. I completely stripped our '67 down. That was about 10-12 years ago, but I do not recall any of the original paint color on the underside, anywhere - other than what I might have considered overspray. Cal
I did my coupe years ago. Just grease and crap and rust. I did the floor on my vert a few years ago and after the grease was removed I found the original paint there. It's like they quickly spray it to seal the factory primer. Top coat for color, but just barely.