Frame number WM20.46372 was despatched from the Birmingham factory on 6/10/1941, as part of military contract C/9310. This was a contract for 9.000 bikes (frame numbers WM20.44213 - WM20.53212).
These are two "sister bikes" (frame numbers WM20.45318 and WM20.45319), so that's how your bike would have looked like:
During the war your bike was transferred to the Australian Army, where the British census number was replaced by the AMF number 30655:
Here's an example of how these bikes were renumbered:
No Vokes filter fitted as original equipment on a 1941 M20...The filter was only factory fitted to the last two contracts of the war and the cut off tank to the last 3 contracts...So, one contract without the filter but with the tank and two with the whole set up...I guess these pictures were taken later after modification....The bike in the first photo doesn't appear to have the cut off tank and the mounting straps for the filter aren't visible either...
I'll stick with my pillion seat for now...Ian