Taylor,
If you have orginal paint on the car make sure you document the color. Often there may be several layers of paint that should be doucmented or saved. Up under the end platform roof overhang is a good place to get this information. If you want more information about doing this check with the restoration staff at either (or both) California State RR Musuem or Nevada State RR Museum.
How you handle a job like this will be the difference between being a preservation organixation and being a tourist railway.
You might also post this inquiry over on the message board "Interchange" at Railway Preservation News. I have seen that board be a good interchange about preservation and restoration practices. One of your Sumpter Valley people got some good information there about doing roofs over at RPyN.
Brian Norden