Take a look at this thread:
I would suggest you talk to Alan at G.A.L. He's an expert at making new sides for the AMS coaches, like this baggage/RPO kit.
If you have a drawing, he or I could probably produce a product DWG file of the Pagosa Springs car. It's not a lot different from the EBT #16 - just needs the doors and windows moved and the roof cupola.
Here's the Rio Grande kit:
Here's the EBT #16 built up pilot model.