....I've thought about this since the first post and maybe, somehow,the bolts that also hold the fenders to the sides were painted to. Back in 70 I became the owner of a 1950 which had belonged to my wife's grandfather. He had purchased it from the original owner which was town mayor. It was a low mileage original and very well cared for.
....I THINK or it seems to me, that the bolts holding the fenders on were painted. That would mean the bed was painted and assembled before going on the truck. Other wise there'd be no paint lower back of cab. Now, that would beg the question of when did the wood and bed strips get painted since they were black?
I agree with Brad, we need a "very original" truck to examine.