particular steam locomotive, I've been able to sort out the sanding gear mystery. My guess was correct, the operating mechanism from the cab only exists on the left hand side of the engine. From a lever on the side of the smokebox a rod goes to the right and pulls from that side.
Of course this throws up more questions - with the operating rod going through the smokebox, how did the holes to let it enter and exit affect steaming ? Why didn't it get covered in ash and muck seizing up ? Maybe it did as the linkage isn't obvious on later photos of this engine.
The sharp eyed will spot that there are two whistles. Apparently there is a normal one and one for the train crew to use, connected to the train with a bit of rope. No. I'm not modelling the rope.
Anyway, this put me into a position to prime the model. This has gone well despite my hairdryer having broken down so I had to rely on normal drying. Time for a new one I think.