I am having difficulty changing the bulbs in my older 60 ft. Williams streamlined observation car.  They are attached to the frame of the car, not the truck.  On the rest of this set of cars, I unscrew the trucks and hold them without damaging the wire, unscrew and carefully slide the frame a few inches, and gently remove the bulb, but this doesn't work for the observation car.

How should I access the bulbs on the observation car?  I would appreciate any suggestions.