It begs the question, 'Is that really the engine number?' I can't find any other entries in the LDMCC machine register with that style of engine number! As the bike seems to consist of both pre 1914 and post 1914 parts, could it be one of the war time machines that were returned to the factory when hostilities ceased, to be refurbished and sold on to the general public? - in which case, could the quoted numbers be part of it's military identity, i.e. JFC - joint forces *****?.
What ever the outcome, the quoted number doesn't conform to the usual style, and isn't in the expected position on the crankcase (on the mag platform, between the mag and rear cylinder).
Regards,
Eddie.