Saw this on a FB group. I like it. Painted this would be pretty sweet. With so many people have spare parts / parts vehicles around, I'm surprised no one has done this yet.
For MJ's it's prob because they're unibody until you get to the 'rails' where the bed bolts. It's actually semi-common for FSJ guys to make j10/j20 crewcabs with a donor waggie and most look pretty sweet (although I think a shortbed would be more proportioned in most cases):