Okay, this has been "fun" so far
Golden Gate Depot has an observation car with the end recessed, as it was on the Blue Comet cars. Only problems are it has 6 wheel trucks, incorrect window spacing and an incorrect interior. The interior will likely be an issue on ALL O scale observation cars, as the Blue Comet had individual movable parlor chairs.
Atlas Trainman O scale Observation cars have the windows correct (it supposedly used a CNJ car as a prototype), but without the recessed ends. It also has 4 wheel trucks. I think that's the way I'm going to go for the observation car. I may or may not move the end back, depending both on how hard it appears to do and how much free time I have and how ambitious I feel. It may just get painted for now, with moving the end a project for a later day.
https://mrr.trains.com/-/media...R0816_10a.jpg?mw=600
The Atlas coaches are close. They still have slightly wider dividers between every other window, but not nearly as bad as Lionel does. I may pick up a set of those for now, and make castings of the thinner dividers and modify them somewhere down the line.
https://cdn.shopify.com/s/file...00x.jpg?v=1541689405