I replaced the boards on my 86 fleet last year.Made new ones out of 1/4" Birch plywood.FWC and ATC will sell you the parts if you don't want to make them yourself.
It 's attached to the hinges with pop rivets.Search on here for lift board replacement.1/4" plywood has worked for me(replaced about 1 year ago).A little patience and lots of drilling and pop riveting are required.I think it took me two days to cut them out,clearcoat/stain& install them.I'll look and see if I have any pics of the install.
After looking at the pics I also replaced the bed boards at the same time
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