The truck, including the box, is a Ford product, not aftermarket. It was built on the 157" wheelbase chassis and the box is 11 feet (132") long.
Read all about it here:
http://aafords.com/open-bodies/express-bodies/197-express/
I'd say the red truck posted above is custom built. It appears to be two 30-31 Ford truck cabs joined to form the crew cab, three pickup length running boards, and a modern bed.