After 35 years in the northeast the cargo area was rusted beyond spot repairs. This is what the truck looked like after all the damaged metal was removed
I purchased a junkyard bed from a Chevy S 10. That became the donor for the rear cargo area. Ironically enough, the measurement in between the wheel wells was identical.
Welded in place. There was no sourcing a solid Toyota bed for the corrugated sheet. This idea Came from my father who suggested we try it on my 04 Tacoma where we grafted in a large section from a Ford ranger bed. This may be helpful to some dealing with a similar circumstance.