It was my understanding that the big bolts shipped from the factory as just a cab sitting on the frame.. the dealer or the buyer of the truck would decide what sort of flatbed/dump/tow truck/box/etc they put on.
So like its been said.. the old '37 took a dump in the pasture, and you need a replacement now.. you take what the dealer has in stock.
If you were just going to put a flatbed on one of those trucks, the 5 window would be usable.
5 Window trucks may not be as common as 3 window trucks, but they certianly are far from being rare.
