That bike seems to have everything that a 39 M20 would have except the speedo drive through the brakeplate.
It appears that it may even have the pre war gloss under the drab, visible where the knee pad has been removed. Is this one 39 or 40? I see he has painted 'Gertie' on the toolbox, a shortened version of the English name 'Gertrude'... Wife, girlfriend, mother or granny I wonder? ...Ian
It looks like a C5110 census number so probably a late 1939 build which makes the presence of darker paint under the knee grip a bit of a puzzle unless the tank is not original ?