R60/6

Why am I seeing some R60/6's advertised with drum front brake and others with the earlier /5 drum

Did BMW fit drums to the early /6 bikes and discs to the later ?

Looks like it

https://www.realoem.com/bmw/enUS/partgrp?id=0251-EUR-01-1974-2476-BMW-R60_6&mg=34

The /5 and /6 600s all had tls drum brakes. These worked well in the dry and the wet, except when stopped facing uphill! When BMW brought in the /7 series (early 77) they changed to a single ss front disc. Not a great idea as they did not work as well as the tls drum. Fashion, accountants ...

If it's advertised as a 60/6 then it really should have a drum. Some people may have changed to a disc. If So, I would suspect a bitsa or a front end shunt.