Here in California, the previous owner of my 1984 M1010 ambulance had problems with San Francisco bay area DMV (Livermore), and they would only license it as a 1 ton pickup, requiring a weight based registration ($280/year). He had to fight with them to get that, they didn't want to title it at all, due to it not having an emissions sticker.
I took it to Hanford DMV to do the title transfer, and they agreed in a body type change to Motorhome, since the rear compartment has passenger seating and windows (and a porta-potti, Engel fridge, and coleman stove will be in there too). Now, as long as I don't run into any issues with the state office (everything went into suspense due to my requesting my amateur radio personalized plate), I should have the registration reduced to less than half. Hanford DMV just checked the box on the form for "no emissions sticker", and noted that it was a diesel. The VIN sticker on the door was intact, and was used for VIN verification (I pointed out the data plate with the stamped VIN as well).
Not sure you need this any more, but I posted this for other's reference. In California, you can go to a DMV office elsewhere, and maybe going to a more rural office may help if you run into issues.
As for insurance, my agent at first thought Allied (Nationwide) would throw a fit, but I pointed out that I had my M715's insured with them no problem, and sure enough it's not an issue. It's listed on my insurance now as "1984 Chevy CUCV M1010", since that's what I told them (the Chevy came from the VIN).