I've managed to persuade my printer to make something without warping this time, though it has come out a bit stripy instead. Hopefully this disappears under a layer of paint. Anyway, the test build is going... well, not ok exactly, but it's working now. I had to adjust the solebars quite a bit to get the axle spacing right, even though I copied the dimensions off a previous kit that worked fine. Some investigation to do there. In the process of doing that, I managed to snap one of them in half, but fortunately I think it has repaired ok.
And yes, that does say 'SER' on the axleboxes... in 0.1mm thick text!