Thanks for the info folks. It's beginning to look as though SOTS is a version or spin off of Fareweel He (Roud 803).

Unfortunately, if SOTS exists anywhere in Greig Duncan, I have failed to find it. To complicate matters there is only one version of FH in there, and that is just the melody and one verse.

I'm starting to suspect that SOTS has never been collected as such, but learned direct from oral tradition by a member of the Scots folk revival. Mary Stewart perhaps?