Hiya
If you browse the stock photos of what Atkinson Vos sell, and their comments as to what they regard as fine/bad/Omygoodness you'll get a good idea.
You sometimes get new take off cabs from mogs when people make something like
http://www.southcavetractors.com/unimog-strac/ but they specifically have one cab that shuttles back and forth. Merc make a new mog using that cab, ship it to the UK dealer who remove it, convert and ship it back. But I know A Vos have had brand new take off cabs from that kind of source in the past, and I've seen one on Mobile.de.
If I had gone down that road I was told the easiest way was to have the new cab directly next to the truck, and just swap bits over so no big confusing pile of stuff to remember what went where!