Guys we are really overthinking this here. The Williams 60 foot aluminum observation car is the same as a Lionel postwar aluminum observation car. On the rear of the car remove the nut behind the dummy coupler/apron. Pull the apron off. Pull the rear roof section with the lights off. Remove the screws from the front vestibule. Remove front vestibule. Slide frame out.
6 days and no one figured it out...