Okay, here is what Joan says about MacCormick in her book The Ross of Mull Granite Quarries, 2nd ed, New Iona Press, 2004:

Neil MacCormick succeeded William Muir as Tormore quarry manager in 1875 and moved into Fionnphort House with his wife Annabella MacLachlan and their large family, of eventually eleven. Neil had been born in Iona in 1836 and shortly afterwards the family moved across to the Ross of Mull. He worked in the quarries from an early age, acquiring great knowledge and technical skill. It is said that his invention of a brake, applied by a lever, to the steep rail which took trucks from the upper Tormore quarry down to the quay became widely known. A memorable event in his life was a visit to Egypt to advise in a dispute about transport methods, which had arisen between the Government there and a firm of London sculptors who had leased a large porphyry quarry.

Neil MacCormick took a close interest in the social and religious life of the community. Besides leading the local choir, he was a precentor in the Free Church and was president of the Band of Hope (later the Temperance Society) which met once a fortnight at Creich School and to which William Vass and quarrymen such as Lachlan MacCormick and Alexander Maclean also belonged. Neil also liked sailing and competing in regattas with his boat the Fairy Queen. Two months before his death in 1925, at the ripe old age of 90, he and Brigadier General Cheape judged the piping competition at the Iona Regatta and Games. A tribute to his memory in the Oban Times of 21 November 1925 was fittingly headed 'A Noble Highlander'.

I have frequently stayed in the quarrymen's cottages at Tormore (which Joan grew up in and still owns). That is probably where MacCormick grew up - Fionnphort House, where he would have written the tune, doesn't exist any more.

This ties a few things together. A missing link might have been Marjorie Kennedy-Fraser - she stayed for a while in the cottage at Tormore just below the one I've stayed in. Joan's father William Caldwell Crawford leased and then bought the cottages just after MacCormick died; he was a painter so may well have been told about the place by Kennedy-Fraser's batty painter friend John Duncan (I'll ask Joan about that). Kennedy-Fraser would have known Neil MacCormick.

MacCormick would also have been happy to see his tune used for the Temperance movement, so maybe the connection goes back a long way. But he would not have been best pleased to see the Catholics getting hold of it.

I think I can dig out a lot more about this.