That's a tough one that is!
Be pretty neat though. Seems to me that I've seen one somewhere, that someone had customized similar to what you're contemplating. But it's been forever and a half since I've seen it, so have no idea where it was.
Problem with fitting one from a later truck is that a lot of the newer stuff has real wide bed-rails. Might not be a big issue, but might change the profile of the edges and how the seals are placed.
Have you checked any other trucks for width yet? Like a Chevy S-10 or Nissan truck maybe? That would seem like a good place to start.
Good luck. Can't wait to see if you have any luck in that regard.
Paul