Alex (@The_Swoose) at Swooze Customs has continued his 5-ton truck conversions with a 3D printed, non-dropside standard bed for the later M813 cargo truck.
CAD images
The parts
The slots for the bows are open as well.
You can find it on eBay
1/35 M813 Bed Conversion | eBay
Earlier M54A1 non-dropside, standard bed too.
1/35 M54A1 Bed Conversion| eBay
I used the M54A1 bed conversion on my Easy Rider guntruck, highly recommended.