reversing gear. Annoyingly I didn't think to take a photograph of the part before I'd fixed it in place so it is now a bit difficult to see how it goes together. This was quite a fiddly part to make as there are three etched parts and some brass wire to be soldered together.
The reversing lever is made of three etched parts; the main lever and the rod the protrudes through the cab wall, and then two toothed gear racks. The three parts are held together by two small pieces of wire that slot through all three parts at both ends of the toothed racks. As I'm sure you can imagine holding all this together is a bit tricky, but worth it as the result is a very fine representation, such a shame really that once the model is finished you'll almost never see it; another good reason for keeping the roof removable.