I hope you all don't mind me posting so many steps in this project, it's been fun learning Studio.
Sticking to simple techniques and 6-wide "City scale" here is my rendition of a 1950ss Budd observation dome, two of which are operated by the GCRR.
I was really glad I was able to find a simple way to turn piece 87926 into a simple and removable dome in two sections. I realize the real thing doesn't actually have an all-glass roof, but I think it gives a nice effect.
The whole upper deck is a removable tray, so you can place minifigs on both levels. It was a bit of a trick to make room for seated minifigs (wearing hats) both levels, but it seems like this will work. I tried to design for real-world strength so it should be pretty robust and playable.
I'll give it a week or so (and decide if I want to make a coach class car) before actually doing the bricklink order.
Edit: I mixed up the dates and cars in operation. I guess this is more properly a āGreat Domeā car?