OK, be pedantic, Snuffy. But seriously, can any evidence be found to suggest this song might commemorate an incident in Montrose' campaign? Or, more specifically, this version of the song. I think it's first recorded appearance is in the context of Derby, rather than Fyvie. And then, of course, there is the rather unlocatable Fennario.
    Montrose definitely has one song going for him, though: he wrote the words for "Never love thee more", whose tune ended up used for "Derwentwater's farewell" 60 years later. Montrose and Derwentwater were both notably loyal to Stuart kings, and both suffered the predictable fatal consequences of honesty and bravery while associating with the Stuart family. Best avoided, I should have thought.