Hey Ken,
I don't know 100%. But I've noticed from part numbers that the last four digits (not all parts) identify the model bike it fits. If the last four are 3000= BS50/60, 5000= BS90/100, 8000= BS175, 9000= BS350. For example: p/n xxxx-5000 would be for the BS90. This theory works with parts that are common to many models like wheel hubs/clutch plates etc. Ex. p/n 2214-9000 fiction plate BS350, p/n 2214-5000 friction plate BS90. If this theory holds it should be for the BS50/60? Hope this isn't too confusing? Steve