I always enjoy outrageous ideas.
I've seen a few pickups made using the lower panels from a Suburban or panel to form a bed, but not one done as an extended or crew cab.
As I picture what you've described I see an extended cab pickup with a short box integrated behind it. Do I see what you are descibing?
I'm imaging this based on a 1/2-ton panel with 116 inch wheel base, not a 1-ton with a 137 inch wheel base. If you start with the longer 1-ton panel you could have a full crew cab and a full size box.
You might enjoy following the link below to my web site and checking out my plans for a COE Suburban Cargo. Not the same as what you describe but outrageous in similar ways.
