There was once a US company USA6x6 that made 6x6 and even 8x8 conversions for trucks, vans, and RVs. I was in contact with the owner over the course of a year and almost took the plunge on a Fuso forward cab rig that would have had a dual floating 4x4 front and rear setup (8x8 with all wheel steering). Unfortunately, or maybe in hindsight, fortunately? the company closed its doors by about 2010.
There is still a company called StarTracks that will do 6x6 conversions on US based (Ford/Chevy/Dodge) trucks or vans.
One of the most famous USA 6x6 builds was the T-Rex seen in this photo at _this link_.
Fun stuff to dream about!
Thom
should have checked the photo links... the above are broken when pasted into this forum ,(