I tried asking this question on the thread about the donation of the 4-6-6-4 and the 2-10-2, but it seems to have been lost among the discussion about the locomotives.

Do we know the identifies and/or heritage of the passenger cars included in this donation?

It is said to be four 1950s coach cars, a diner-Lounge car, and a baggage car.

Plus two business cars: "Two business cars: the Selma, previously Western Pacific's Feather River, and the Stanford, originally the 1928 Southern Pacific Sunset" but I'm guessing you saw that, I haven't seen any other specification.

Do not quote me on this, for I am not sure myself. I think I read somewhere that the four coaches are part of the steam fleet, and the remaining cars were simply "scattered" at the Wyoming roundhouse. So, something tells me that one of the Daylight MOW cars
and other scattered cars (ex-C&NW?) around the roundhouse might be going to Silvis.

But again, I have no credible proof to back this up so please take what I say with more than just a grain of salt. Maybe the whole salt-shaker and a black cat too!

Western Pacific car Feather River was UP 109. It was purchased by WP in 1971. It was built for the train Overland in 1912. I believe that the UP passenger cars that are still used are much newer. The Feather River is 110 years old and there could be all kinds of issued. When I worked for the WP the roof was leaking and I was told to fix it, so I had a foam roof put on the car. It appears from the pictures that the foam roof is still there. The trucks were changed for roller bearing trucks that CMO Bob Mustard got off a New Haven baggage car. Marketing put a lot of miles on the car and it always needed work of some kind. When Mike Flannery went to the MoPac as their President about a year prior to the merger, he took the car with him.