Drivers license requirements

We are in the process of purchasing a 2006 Fleetwood Revolution 40LE. California requires a non-commercial class B license for motorhomes over 40ft. The Fleetwood brochure list the "bumper to bumper" length as 40'11" . In the same brochure both models 40J and 40L are listed as 39'11" overall length. All three models are riding on the spartan liberty chassis. For licensing purposes what length controls, the model designation or measured length?

I appreciate feedback from someone knowledgeable about this subject

Thank you