Alan, I spotted your query first on the NOC forum. This is what I posted there;-
A Serial number as high as 41919 indicates wartime production, thus WD. This is backed up by the other stamping. 'B14' indicates a Base Workshop, 'MS' almost certainly Ministry of Supply and the final part would usually relate to a date, generally month and year.
Presumably fitted with a bushed gearchange shaft and brass gear position indicator ?
The major pricing factor with these is the condition of the top fork and bottom lug.