Below, from left to right, are the shoulder "bars", shoulder buttons and under shoulder details.
Below, this is how they all look like mounted on the shoulder. Kudos to Ryan for producing these!
Another new arrival comes from Jerry C. These are metal backplates to the Utility Arm Carrier (UAC). I bought one for each droid. They are painted black so they do not stand out behind the utility arms.
Finally, here's how they look bolted into the back of the UAC...