The interior height of several finished NCV3 Sprinter conversions is given as 75" or 76", which is pretty much in line with official "maximum standing height" of 76.4". To get this height, though, you'll need to use a thin flooring and put the ceiling cover right onto the ribs. Figure to lose nearly an inch if you get and keep the cargo floor option and cover over that (which is often done to make attaching things much easier than screwing through the metal floor).
Here's another problem, though . . . you're unlikely to want to put that contraption dead center in the van, and the Sprinter has a big difference in width between the floor and the ceiling. If you fit your device so it's at the side wall at the ceiling, it'll be half-a-foot away from the wall at the floor. You can get a good idea of what's going on by looking at this photo they put on the Mercedes Benz of Chandler website of the view through the rear doors of a 2014 Crew van:
The Sprinter's substantial "tumblehome" is a considerable annoyance. When you build overhead cabinets, for example, their width at the bottom is a lot wider than at the top, making it tough to store even routine stuff.
The furniture thing you found is cool; maybe we can get a volume discount. Though we then may need to build our own rectilinear cabins to put on the 4x4 cab and chassis for it to work.
