The company i work for, used to do similar conversions to Unimogs and other small 4wd trucks (rwd axle was removed so the truck had to have a front wheel drive axle)
In this design the wheels werent extendible from under the bed, but the truck was cut off behind the cab and a U frame was attached to it: the wheels were placed underneath that U frame, so when the air suspension was lowered you could drive under a rail of a container, and when lifting the suspension you could pick up that container.
There was also a variant with a flat floor, very useful to load forklifts, and scissor manlifts because of the low ground clearance.
I guess this is an early Ruthmann conversion from Germany, they still make them this way:
http://www.ruthmann.de/main.php?target=funktion_diagonal&lang=en
There are also other variants, without the extendible width axle (more durable)
RUTHMANN: Steiger - Cargoloader - Versalift - Service
Off course, the cheapest versions are based on a lightweight front wheel drive van, like a Ford Transit, VW Transporter, Peugeot Boxer. When going heavier, you need a 4wd truck as a base for this conversion which makes the whole deal a lot more expensive.
Perhaps someone is interested in a ruthmann rear end behind an F350 or 3500 ??