Just completed this task a few months ago on my ‘46 Restoration. We used the saw horse support method and it worked like a charm. Once it was all assembled it was slid onto the chassis using 2x6’s to span the distance between the saw horse supports and the frame rails. It helped that the rest of the truck was on tire skates, so we could more easily line up the bed. Once the bed was on the chassis, bolt holes were lined up with large tapered punches. Two of us accomplished the whole task in less than 8 hours. Your truck bed might be a bit heavier than this one.