I have a 67 and a 70. I notice that the 70 has no paint under the dash, floors, etc but the 67 does. I don't think they started dipping bodies until much later and imagine these were hand sprayed. It appears they stopped doing the inside at some point, likely to save a few pennies. Any historians know? And did it vary by plant?
Not sure you can make a determination based on two cars built 3 years apart. Likely even made in different plants. Probably just two different painters one less high than the other or with less of a hangover. If GM could save 5 cents per car by not painting the upper half of a brake pedal, they did it.
Flint used Gray or black primers where GMAD plants used various shades of reddish brown. I have seen grayish primers on the floors and under dash of my Flint cars. It wasn’t heavy but I wouldn’t say it was bare.
My California car is brown....as in surface rust! I guess they figured nothing rusts on the left coast so why paint it!
Fremont plant paint line (from ultra-high-compression.com): "Vehicles receive gleaming exterior finishes in Fremonts state of the art spray booths. The large volume of air supplied to each booth, sufficient for 300 average sized homes, is electro-statically filtered. Temperature and humidity of incoming air was also closely controlled. Notice on this Cutlass hardtop the overspray and chalk marks on the firewall. The firewall was then blacked out after the paint process, thus covering up the marks and the overspray."
Interesting statement about the chalk marks, and very true. In my 45 in the restoration business, 95% or more of the chalk marks I have found on these cars have been under the black just like it is stated in the above post, yet every show I go to people have put the chalk marks on top of the black. If I don't find them on top of the black, I don't put them back on that way.
My Fremont firewall is body color; I figure it's an oddity given it was special order job and the only A body painted that color at that plant that year.