[Spruce]

The point of Duluth/Superior is as far west as the Vikings could have possibly landed. Totally possible.
But. That area is Ojibwe.
The first Ojibwe records of white men is frencmen from the south. Not Vikings from the water.
No way anyone made it past them. Which raises my main doubt in the K. Stone. There is NO WAY the Ojibwe would have allowed it to happen. No way.

[Fedora]

That's a good issue you raise, but what I wonder with respect to that is when the Ojibwe (Chippewa) first became entrenched where they were when the French arrived? Our records of them come from relatively late compared to the Vikings and don't tell us much about their prehistory, to my best recollection (was reading about this a couple months ago, though I may need to refresh my memory on specifics--just returned the book to the library today actually, per Murphy's Law--doh!). There was a lot of displacement going on during that period due to migrations caused by wars with the Iroquois.