Lance would likely be sold that truck as an incomplete vehicle and become, if he is not already, a licensed upfitter. That truck is then re-sold as an RV or a reefer truck or whatever the upfitter calls it.
The changes that are made by the upfitter or body builder cannot adversely affect emission equipment, crash-worthiness, etc. As I understand it, the end user, is basically purchasing an "Earthcruiser XD" or whatever they decide to call it and THAT is the complete vehicle, not the vehicle that was purchased from the dealer as a chassis cab.
It may not be exactly the same as a chassis purchased for ambulance construction, etc., but installing an NV263 transfer case from a 2500 Silverado and a DynaTrac D60, would necessitate crash and emissions testing for the truck in that exact configuration.
A possible work around would be to sell the truck complete in 2WD, then have a "third party" perform the 4x4 conversion, post registration. This third party would conveniently be located right down the street so the customer is not inconvenienced by travelling a long distance to have work performed on their newly delivered EC
I am aware of several "kit car" companies that sell $100K cars in the US, without an engine and trans. Those are installed by the aforementioned third party.
Reduce, Reuse, Recycle - buy a (cheaper) used truck, toss the awful PZ motor and Duonic trans, and swap in your favourite LS series crate engine, all without EPA interference.