Don – it would be worth you joining the Drummond lathes group on Yahoo, a lot of folk on that group with much knowledge about Drummond lathes and their history.
As far as I know the "B" was produced from 1912 to 1921, when it was replaced by the "M" type, so you're looking at a 9 year period with WW1 in the middle when I believe the numbering system got a bit confused – it looks as though your number is a digit short!