There were "seats" on the forward cab and not the rear one. No idea why. I didn't see them offered as parts. They aren't much to speak of. I didn't order the "people" and it looks like I'll need to find some really small ones to fit 
There is an X-Ray view of the prototype here:
Lionel took some liberties with the interior arrangement. I am guessing that something was stashed between the engineer and firman sides and the control panel was used to hide it. On the Williams engines the two can motors are just about where the main transformer (front cab) and train boiler (rear cab) would be situated. I BELIEVE that if you were to go through either door on the engine sides you could go along a walkway between the front and rear cabs and I KNOW that you could walk across the cab locations from engineer to fireman station.
It looks like the compartments for the main transformer and the train boiler were separate, located dead center, and each had a single doorway at the back of the respective cab. It looks like there was an access door at the front of the cabs to get access to motor control units 1 and 3 that were located under the long hoods just in front of the cabs. I think the front doors on the extreme ends of the hood only allowed access to the main ventilation blowers?
