SouWest Hi, Bob: I believe that they were from Precision Scale in Montana. I've used their interiors for other projects as well. They make them in various colors of plastic and in various seating configurations. You're talking about the Skytop, right? The interiors or the Superdome are all the original seats, just repainted and relocated. I had a photo of one of the Superdome interiors and it showed the seats to be a reddish, almost maroon color. That color you see is as close as I could find on my spray paint shelf.
Speaking of Precision Scale, I also used their seats in some Weaver smooth side, 1934 Milwaukee Road built cars. When Weaver did them, being on a limited budget, they simply used the interiors from their Pullman-Bradley cars. I had always wanted a train made up of those cars and felt that I'd never have another chance to own a set, so, in spite of their shortcomings, I bought the train, some seven cars worth. This has always been my favorite passenger train and is the train that Lionel should have made in 1935 when they came out with their original Hi but with the articulated, M10,000 cars. So I bought them and started upgrading the interiors as well as adding detail to the undersides of the cars. Also put an interior in the Tip Top Tap car. Unfortunately the windows on the Weaver cars appear to be a bit low, in spite of the fact that they look pretty correct. So I had to lower the floors a bit and even then the seats were too high for the window openings. So I had to maually cut some of the seat pedestals off. A lot of work and no one that visits the layout even notices, except me! And that makes all the work worthwhile.
I'm also working on a ten car train of the 1938 built rib sided cars from Weaver. But these cars were from the early 1990's and were built before it became standard to include interiors. These trains had more variety of car configuration than the 1934 series, so a lot of research has been necessary. As of yet, I only have two of the ten cars so modified.
For people (My trains are always full: My railroad makes money!) I've been using the 1930's 1940's seated people from 3rd Rail. These people look appropriate for all these trains. The men are all wearing suits and ties, some have hats and the women are all wearing skirts or suits and most are wearing hats. That's the right way to travel; none of these jeans, cut offs and other sloppy dressers you see today.
Paul Fischer