Afraid you're a bit late about the legs - that theory gets quoted in most Mainecoon books (in spite of being biologically impossible and debunked at least 140 years ago)!
As the origins of the Norwegian Forest Cat are as obscure as the Mainecoon, saying Mainecoons are descendants of Norwegian Forest cats doesn't get you much further!
Doubt if the Vikings as such were responsible, the Viking settlements in Newfoundland were rather short lived and before the probable date of development of the Norwegian Forest cat. Only thing for sure about both breeds is that they are descendants of a male and a female cat.