That’s another very fine job of research and modeling the prototype.
Later on and in case the comparison might be useful I’ll post pictures of my own different approach to creating an observation car interior based on the same basic K-Line assembly your car has. First, as general points:
1. It’s interesting that you have found the basic similarity between the K-Line interior and the “Cascade” prototype. K-Line and then Lionel used that interior assembly in innumerable boat-tail observation cars in just about all the railroad liveries they produced - in Lionel’s case until the 21” ABS cars started to be made. My research did not disclose the source of the K-Line design but then I have not worked on UP cars before.
2. What it did disclose was that the interior colors and furniture arrangement of cars of this kind changed often over their service life. You’ll also find that with dome and dining cars.
Thanks for posting this very interesting series.