Peter: I'm modeling the same era Empire Builder, and the CZ dome-obs appeared in it on rare occasions. But I already have the other CB&Q cars I can use, so won't be buying the set. The EB didn't use E's in Montana, so that's no help.
I could use the CB&Q's third style of 10-6 sleeper, but nobody makes those, in any scale, as far as I know. These were the 1956 cars for the Denver Zephyr, which had the six double bedrooms in the middle, instead of roomettes at one end and bedrooms at the other. 4R-6DB-6R was probably unique.