You got my curiosity up with your pic. I had to go look at my early 71 since I didn't remember anything being there. And, nope, no wing nut/bolt there. Everything else is the same though. What you have there must have been added by a PO, for whatever reason.
I have a 69 with that spare tire carrier. No wing nut on mine but I was wondering if you know how the carrier is supposed to stay closed. I have to use some bungee cords right now to keep it from sinning open.