[FortyNiner]

I have not seen any original spec information for the Bonus Built truck paint. Good on you for installing an original style metal bed.

I can only offer conjecture. If the metal beds were welded to the bed sides, that would have to be prior to factory paint. While possible, masking didn't seem to be a practice of that time. So, in my view, either the bed floors were completely painted or only covered with overspray.

FWIW, the metal bed floor on my 49 also didn't show any sign of paint. Time had also taken its toll.

The sales brochures of the period that I could find don't typically show the bed floor, so no help with the question.

I'll keep poking around and report any findings.