As far as I know, the two UP cars were just other roadnames issued around the same time as the rest.
There is nothing special about them and they are not even close to any UP business cars - except marginally similar to the Sunset, an ex-SP car. The Sunset was actually longer, had a different wheel arrangement and 2 3 axle trucks. It is currently painted yellow to match the UP fleet.
It's the worst kept secret on earth that Kato is doing the heritage fleet business cars in N - probably within the next 6 months, so just hang on and get the real McCoy. (People were around when Kato was measuring the cars....)
- Lou