I e-mailed the guy who wrote the CL ad response to see what he had to say. My understanding is that all of this regulation (at this point) is just for COMMERCIAL diesel vehicles. The guy who wrote the ad says that the Detroits are commercial diesel vehicles because they were originally registered as buses although I don't believe the California DMV sees it that way. These are specifically mentioned as non-commercial vehicles on the DMV website:

Housecars or Motorhomes (CVC §§260, 362)

A motor vehicle originally designed or permanently- altered and equipped for human habitation.

Note: Truck tractors as defined in CVC §655 that have been:

Initially manufactured.
Modified by a second stage manufacturer.
Otherwise altered to include living quarters,
are considered commercial vehicles under CVC §260, unless the living quarters permanently prevent the truck tractor from towing or drawing other vehicles.

Trailer Coaches

Trailer coaches may transport property, but are designed primarily for human habitation or human occupancy.

Dkr.