Another thought - there may well be some evidence of the chapel that was dedicated to St. Mardoc. Placename evidence.
I notice on CanMap that the stone is across the modern A9 from an area called "Kilmorich" - "kil", of course, signifies a church. In 1246, a church was founded at the head of Loch Fyne which was dedicated to St Mordac - it was called "Kilmorich", so it could be that this Kilmorich has the same origin?
Circumstantial again, but interesting (to people like me who like placenames, anyway).