Thanks, everyone, for your responses! After much thought, I've decided that I'll be building my cars in their B&B configurations rather than their passenger service condition. Not only is it more faithful to my chosen era (roughly 1938 to 1945, bracketed by a brass model of RGS #25 and a Wayne bus-bodied Galloping Goose) but I think they'll make more interesting models.
I'll be on the prowl for a 3-pack of Blackstone Chili Line coaches if I choose to do the CCC special.
In the meantime, thanks for helping fill the gaps in my understanding of how passenger service on the RGS worked just before the Geese took over.