I pulled the rear drum wheel to allow removal of the rear miter box, override and driveshaft. Turns out the rear drumwheel has an iron or steel insert for a drum brake. The brake drum measures 6.000″ inside diameter by 1.4375″ wide so I suspect this is for a USA made brake not a metric European brake like the Ducatis on our MK1 bikes. There is no provision for an anti rotation bracket like there is on the front fork.
Here is the front and back of the Aluminum dust cover that is probably the source of the squeaking that I heard since it was rubbing the brake drum insert at one spot. I can easily remove the offending dent. The dust cover is stationary and is retained between an inner axle spacer and the fork.