This is frickin' sweet. I solved the problem by buying a Panamera.
I have a "Will-Wood" (??) hitch I mounted on my 986.2 Box and have been thinking about how to modify it to accommodate a smaller 1-Up hitch. I had thought of just cutting the aluminum impact bumper to allow the hitch rack to slide deeper into the receiver but haven't done it yet. Primarily because I wasn't sure how/if I could get a keeper pin into the hitch.
If you're relying only on the expansion ball in the 1-Up hitch, are you not concerned that it could loosen and leave your bike on the road behind you?
(I have the larger 1-Up rack on the Pano. They're sweet. But I'd like to be able to run a hitch rack on the Box during the summer.)
BTW, super clean install. Absolutely excellent work. Thanks for posting.