I'd start will potbellied coal stoves. Relatively cheap, primitive, simple, but probably satisfactory for the C&TS's immediate needs. And they would add historic ambience to the cars. Propane stoves would could also work, but I'm not sure would be worth the extra cost and complexity.
Clearly if the heaters are expected to be used regularly, and routine comfort becomes a bigger issue, something like the Baker system would probably be best. But initial cost and maintenance cost then goes way up.
Electic heat is a turn off to me, because somewhere there is going to be a motor going put put put....
If I remember correctly the WP&Y uses propane stoves, the Nevada Northern uses wood pellet stoves (quite sophisticated, and need battery power).
Question. Are all the enclosed Silverton coaches heated, and if so do all of them have the circulating water system....or what else. On the older cars is this basically the system that was put in for the San Juan? And is the system in the newer cars the same?