I would guess on my 57 bigbolt, the markings were put on the firewall when it was a bare cab. To designate what options or deletes the truck got. For example: Down behind the engine it has (STD) probably standard trans. Then up higher on the left side of the firewall, it says: (deluxe heater) The rest of the numbers mean nothing to me, except it did come (delete radio, passenger sunvisor, armrests, cig lighter & rear view mirror.)
All this was not written on the firewall, just a bunch of numbers.
