It looks similar to a 1930 model DL of 500cc (frame, forks and gearbox), but not quite exactly the right engine for this.
Anyway, the saddle tank, hand shift and upright engine make it a 1928 to 1930 model, maybe a 1930 350cc C?
Come on you RE buffs out there and help this man out!
In any case it should be quite rare a model, so could be worth something to the RE enthusiast.