Well I finally called Polycomposit.
What a wonderfully helpful chap!
The Cabstars are officially Nissan guaranteed and homologated 4x4 versions. Nissan are finishing the homologation of the 2008/2009 model; the 2007/2008 models are almost sold out (there was one left when I called on the 17/12/08). They come with a LSD standard rear and optional lockers.
So for the French market Polycomposit can supply a Cabstar with a 4 metre long box in the back, fitted and furnished for real off road use and stay under the 3.5 tonne mark! The German legislation allows the Cabstar to run up to 4.5 tonnes.
The over cab bed unit in the photo is the owner’s and he doesn’t mind taking the box off if he needs to access the engine; it’s a tilt cab. (kind of says something about his confidence in Nissan’s reliability) He’s not too keen on selling that configuration to a customer.
The double cab is apparently not a tilt, you access the engine from inside.
The SRW setup is available if you specify rims over 100 mm wide, narrower that that and you have to run twins. He assures me that a 9 x 16 goes on SRW without any mods. He can get a huge variety of rim widths.
Engines are available up to 160 hp homologated, but apparently you can chip them higher (I’m not going to get into the whole electronics argument but we’re talking about a truck, not a car, and the design philosophy is completely different; truck fleet buyers expect 0.5Mkm trouble free, so truck manufacturers concentrate more on reliability than car manufacturers)

Price? Well the last 2007/8 cabstar is going for around 40k€, it’s white, 130 hp end currently on twins at the back. All in with a box on the lines of their “grand large” model the price starts around 80k€ and goes up depending on tanks, underbody protection, interior gadgets etc.
He said that although they are supposed to charge for a change in the interior layout, if it’s a simple rearrangement (rather than a big addition) they don’t bother to charge the difference.
He said the new 2008/9 4x4 cabstars will be somewhere between 55 to 60 k€ depending on options.
The guy’s a 4x4 enthusiast, and being in the trade he can get his hands on some lovely off-roading accessories.

He also mentioned that for a slightly bigger vehicle the Athleon is also available in an official 4x4 version.

As the photos on his site suggest he’s perfectly happy to build you a box for your own truck, new or old. He always uses a torsion free mounting but didn’t want to tell me the secret of his version.

Food for thought.

As I mentioned, I only live an hour away from Polycomposit. If anyone would like my help (linguistic for example) to deal with them, I would be happy to use you as an excuse to go and visit the factory.

Cheers
Luke