Rear Wheel Axle (shims, Washers)

Whilst that may work I would prefer to use a more stock / sturdy solution in the first instance

 

Mine just uses an 8mm caphead bolt through the rod-end with a spacer between it and the caliper, though it is not an OEM Ducati part.

 

^ that bike is lovely DD, a real credit to you!

 

DD will probably look to do the same thing as you then. Finally got a 5 spoke wheel so back to the powder coaters I go!