Forgot I had this one on my old '85 pickup. It was welded directly to the roll cage. The rear part of the cage however was removable. The main hoop directly behind the cab was welded to the flatbed with tabs across the top where the runners and rear hoop portion were attached. By removing the rear part of the cage/rack, I could still have an open flat deck to carry larger objects if necessary.
Simple 1" tube for the rack with expanded metal floor.
This photo shows the attachment point for the rear of the cage. You can see the mounts on the main hoop and also the bottom of the rear legs that unbolted from the flatbed.