Bill,
I'm uncertain of what measurement you want to arrive at the amount of living space.
For the "cab" itself, do you want the length from the front bumper to the rear edge of the driver's side door?
We use the entire inside length of the coach from the front windshield to to rear wall of the bathroom while we are camped. I can measure that if you think it would be useful to you.
The passenger seat turns around, we store items on and around the drivers seat, and we have a small table that straddles the engine cover to provide counter space there.
I would be cautious in using any "stated length" of different models in determining "living area" as I have found them to be inaccurate in many cases.
--Bruce