I was browsing Hemmings and came across this article on the F-100 XL. It's from 2012, so probably many have seen it, but I hadn't. My search didn't uncover anything in the forum, so I'll post the link in case others want to read it. Nice read. I remember seeing a one (clone?) for sale on the web, but don't remember it being a unibody.
Light-Duty Heavyweight | Hemmings Motor News

 

Here's some more info on it.


F-100 XL Drag Pickup


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Notice the F100XL is also a big window shortbox!

 

I love the big window uni. I wish mine was one, but I don't think they are readily available.