All of my White Pass stuff is boxed up in storage so I could be wrong.
I want to say most of the trucks the passenger coaches ride on are six feet in length. They also have roller bearings.
I am pretty sure this is true for modern, steel coaches. As to the coaches in question, I don't know.
The White Pass operated trains of 70 to 100 cars in length, depending on where the train was operating and if the cars were loaded or not.
The older wooden frame cars were either scrapped or broke in half. The steel underframed cars from the Colorado & Southern were largely converted into container flats when the White Pass containerized their operations. These conversions did not last too long before the frames cracked, derailments, etc. Friction bearings were frowned on as well. In 1969 the entire fleet of freight cars was upgraded. Most of the cars by that time had roller bearings. There were some older Bettendorf trucks with friction bearings, but they were in the minority.
Right up until the end of freight operations in the early 1980s the White Pass ran mixed freights. Imagine sitting in a coach at the end of a sixty or seventy car freight. I would imagine the operations people didn't want friction bearing trucks under the coaches on those trains.
Someone more knowledgeable than me can correct any mistakes I have made in this post.