Concerning the Clan Gunn origin myth
I've just bought the book 'Warriors of the Word - the World of the Scottish Highlanders by Michael Newton. He was a lecturer in the Celtic Studies Department of the St Francis Xavier University in Nova Scotia at the time the book was published by Birlinn in 2009. I found it at Bookstore Brierlow Bar just out of Buxton, Derbyshire - a great bookshop with the majority at remainder prices.
There is much to absorb from this text and a lot of it applies to Clan Gunn history, including the Clan Gunn origin myth. For example -
People all around the world have an inherent interest in their origins and display great creativity when attempting to explain the present in terms of the past. Although the specific of the origin myths of people change according to circumstance, they tend to reflect several common ideas and concerns. First they are rooted in the deep past to provide a sense of solidarity and historical continuity for people who may be heterogeneous in reality. Second, these myths usually connect their ethnonym with the name of of an historic character on the basis of similarity in sound. Third, origin myths seek to raise the prestige of the group by choosing a high-status legendary founder. Because of their ideological purposes, origin myths always tell us a great deal about the perceptions of the people who create them... (page 55)
The above sums up the Clan Gunn origin myth extremely well; there is no historical support for the idea that the Clan Gunn descends from the deep past of Snaekoll Gunnison and the Orkney islands, it's just his name sounds the same and he was of high status.