A quick update following the longer post last week. The motion is complete, though the crankpin "nuts" have not been finally soldered in place as there will be a further disassembly in the near future.

The motion runs nicely and because it is difficult to show this without making a short movie I decided to time one revolution of the drivers at the slowest setting on my cheap Hornby analog controller (the one that comes with a boxed set).

22.5 seconds with no hesitation. Edit: This from the 5 pole Airfix upgraded XO-4 motor

I am not sure what scale speed that would be but it is slow enough for crawling around an MPD. It will be interesting to see how it runs with a TCS decoder installed.