Thanks! Yes I can confirm the part #447-310-04-00-MBZ from Pelican Parts (called "Trailer Coupling" in their system) did come with the necessary installation hardware (nuts, bolts and washers), and the backing plates. The bolts that arrived are the same as the type holding my tow hook that I removed during the hitch installation. It all arrived in a single box with the installation hardware included in a plastic bag inside (arrived this week, in August 2020).
Note: I didn't use the backing plates in my hitch installation because they seemed unnecessary - in fact they would have limited the amount of thread the bolts would be able to grab, thereby weakening the system imo.
Also note: It took 5 business days for Pelican to get the part to their warehouse in Los Angeles, then took 2 business days to ship it to me in Northern California. The part description says it weighs 11lbs, but I ignored that, and the box indeed weighed more. Sure enough, when it arrived it was the genuine Mercedes part with the "Westfalia" sticker affixed to the hitch's plug hanger (as discussed by others earlier in this thread).