No chance of getting ahold of the nut... like I said, it seems to be held captive in a "sheet metal box". I can feel the edge of it spinning, but I can't get to any of the other sides or the top of it. The end of the bolt comes through the heavy sheet metal that is above the nut.
It really doesn't make sense to me! I can't fit my head between the steering rack and the drive shaft to look and it was too dark at the time to see anything in a mirror, so I'm stuck guessing at what's up there by what I can see (just the edge of the assembly) and what I can feel (and it's not easy getting your fingers up there).
My only thought is that maybe they wanted the nut to be able to "float" side-to-side, so it would align itself with the bolt coming through from below, but not rotate so you wouldn't have to hold it from above. Why else would you not weld the nut to the frame rail? The nuts for the side bushing on the control arm are welded in place.
I couldn't get any official answers late Saturday or today. Hopefully I can talk with someone Monday. I'll let you know what I find!