The NRT 747-400 parks briefly at MSP in the late morning usually around G-3/4. (The long-haul international flights come and go from gates G1-6.) It's easy to find a half dozen or more at NRT if you fly SkyTeam through there. At DTW, look around the middle of the long A terminal near the big SC and big security entrance, roughly gates A34-44.

I once flew a 747 from ORD to MSP on a spring Friday afternoon (i.e., many prime business travelers paying the full FastTrack fares) when many earlier flights had been cancelled due to high winds. On that day, NW pulled an old reserve 747 out of the hanger at MSP and flew it to ORD empty (I was told) to save hundreds of stranded passengers. I was given an upper deck seat and I remember a classic 1960s light fixture over the circular staircase, plus tiny bins for carry-on luggage. Later that summer, I flew in the nose of the same plane from MSP to SFO or LAX after our plane (DC-10, IIRC) had mechanical problems. I think an earlier flight that day had been cancelled also.