The season 6B idea can't be used for The Two Doctors since the Doctor said they just dropped off Victoria so it has to happen before season six, that in an of itself makes little sense given other dialogue in the story, but there you go.
No, because in 6B it was Jaime and Victoria who the Doctor retrieved. Exactly why Victoria and not Zoe I'm not clear.
Far from being "fan retcon", as noted, Terrance Dicks - who was the script editor during the Pertwee era - was one of the people behind the "6B" scenario. So that makes it more than fan fic, and several novels were written based on this continuity, plus as noted a good portion of the Troughton TV Comic run takes place in here.
As for The Two Doctors, I thought the story was fine. And I had no problem with the lack of interaction because it minimizes the necessity of suspending disbelief regarding Six not remembering what happened to Two.
As for the gripe above regarding Nicola Bryant's attempt at an American accent, I have only 6 words: Dick Van Dyke in Mary Poppins.

Alex