It does seem that "Dunvegan" is either mondegreen as suggested by Murray, or conscious adjustment to suit the preference of a singer - perhaps with a soft spot for Dunvegan.

I started this thread with a clear preference for the Tannahill Weavers' version. Possibly due to repeated listening during the analytical process I have now developed a strong preference for Archie Fisher's solo version! Consequently I have also modified my preference from "Dunvegan" to "Eigg". As that seems likely to be the original wording, I am now able to sing it with a clear conscience!

This exploration process is enormous fun. I live and learn. :-)