On my '37 restoration I purchased a complete bed kit from Mar-K. The kit came with detailed instructions for assembly, which was mostly done off the truck. You place the box on the truck before most of the wood and strips are installed, and before fenders and tailgate are attached, so it was pretty easy for me and another guy to lift it on the frame. Your bed would be heavier since it is longer but I still think two people could easily do that.
I would bet that if you purchase your needed panels, tailgate, cross sills, mounting blocks and bed wood from Mar-K, they would supply instructions for your '53 bed that will be detailed enough. Give them a call,
Regards,
Kent
