Quick note: I've occasionally gotten interested in modeling the Southern Pacific passenger trains that went from San Jose to Los Gatos. Part of the fun and challenge is figuring out which cars actually ran on the Santa Cruz branch, and figuring out how to make models of those from available plastic, resin, and brass models.
Jason Hill is now sharing how he's customized existing models to match many of the trains going over Tehachapi Pass. Check out his Night Owl Modeler website to see his projects, including his recent work on a baggage / railroad post office car. Jason also has an illustrated guide to Southern Pacific passenger cars where he describes good starting points for each car.
Jason's interest in Railroad Post Office cars convinced me to learn a bit more about mail service over the Santa Cruz Mountains. In the 1930's, one train a day carried a Railway Post Office car. Inside, U.S. Mail clerks sorted mail and distributed it to the towns along the route. Here's hoping I can find some good details on the mail service!