My Siemens blower motor unit had SIEMENS molded into the plastic end cap that holds the motor unit in the blower housing. The end cap is attached to the motor with two screws (vs. one for the Bosch unit) and the connector the wiring harness plugs into uses a screw (or screws) as a retainer vs. a metal clip for the Bosch unit.
In the other thread where we discussed this, someone noted that Mercedes used a variety of motors in the W123. I assume the Bosch motor was used the most, but I wouldn't be surprised if a third motor variety was lurking out there...BMW used a Sophica in their 5 series about the same time, so who knows?
The motor that Worldpac vendors such as Fastlane offers is the Bosch motor...so a picture of that one is readily available. Here's a link.
http://img.eautopartscatalog.com/live/R301027212BOS.JPG Note that the brushes/commutator are at the end opposite the fan. The brushes are at the fan end of the Siemens motor and inaccessible if you don't remove the fan from the armature shaft.
The Siemens motor has huge brushes, so brush wear and correspondingly commutator wear are drastically reduced over the Bosch motor. If you have a working Siemens motor in your car I'd see no need to keep a spare lying around.
BTW, I just swapped out the parking brake shoes in my '82 300td, so I had a refresher in drum brakes myself.
Russ M