Many of the markings are the same as the codes on the trim tags , Flint and KC
cars have these! alot of the time. On some of the GS's that I have parted you could still see them!
Also the unit number , line inspector initials, and other assembly line markings.
On my GS ( KC Built) you could still see the W for tinted windshield, the 2L for 4 speed, also a R/C in
both corners for the white painted top and red bottom (hidden by fender), unit number,
inspector intials! I will see if I can scan the pics of the firewall when I took my car apart!