I looked through my collection of very small format red hard bound books, and found three on passenger car heating systems. I haven't looked at them in detail, but I've seen enough to think they may be of some use.
Two of them are off of the PRR --- 1896 and 1920. The 1896 book describes the Baker heating system in some detail, and has a drawing of one. The third one was published by the Gold Car Heating & Lighting Co. in 1913. Looks like they had a system much like the Baker.
I would be happy to share this info.