Inspector M89 stayed at the BSA factory in the (late) 1939 - (early) 1940 period. I have these examples in my Register:
KM20.1376, KC10.1779, WC10.552, WC10.583, WC10.720, WM20.11612.
The next one in my list is WM20.20576, with acceptance marking M^65.
So far as the bike is concerned I plan to keep it mostly as is ‘ex government’ trim. It appears to have been black since it’s wartime use except for the green tank panels which look to have been added later. I am quite happy with its current engine for now as it’s original engine JM23 159 is unlikely to be found or any JM23 engine for that matter. I may think about fitting a later B/M ohv engine one day.