We have little to go on - but something is something wrong with the SN Plate. '17' most definitely is a cutting width signifier of 17" - not 20". 'B' is for Briggs, and the last 'D' might be double roller? Does the machine have two clutches?
If the engine is original, Briggs' Model, Type, Code is as close as you'll get to production year.
Unfortunately we do not have a lot of info. on the Alroh.
