Alan, thanks for sharing the song with me. I had only one addendum to your lyrics:

on the estates along Tentsmuir

I'm not surprised either. I would assume the writer likely made the song soon after the disaster, before an official list of names was released.

The Kielland incident dates the song to post-March 1980. Assuming, since the Mr. Johnston in question is, in fact, fictitious, it would follow that the artist based it off someone they knew, or themselves. From this, the geography in the song strongly suggests the singer is from Northern Scotland.

You may also have some luck reaching out to the following website: https://disastersongs.ca/alexander-l-kielland-1980-song/.
At the very least, they're requested songs about the incident on mudcat here before back in 2014