[68C15]

Brandonh has a thread about '68 with no option sticker. I also have a 68 GMC 1/2 ton with no option sticker. now I know for a fact that it never had one, I asked the PO/OO about it & he said the glovebox cover is original. doesnt have a sticker on the back of drivers door either. but it does have crayon like markings on top of firewall starting above heater that says 'CS1590D' '306' 'AR' '4026'. anyone know what this means? will try to post pics soo as possible.