Steve D has posted the answer to the set of mystery pictures on Burnsland. You can read it here. Meanwhile, I am making small adjustments here and there on my Holliday model.
Here’s the speedometer conduit wiring (highlighted blue). The junction box under the right running board “plugs” into the tender.
I also changed out the try-cock funnel into a more traditional funnel shape, and extended the boiler jacket down to the oil can shelf.
Here’s just one of the many subtle details: the curved cylinder cover: