Hi Dan,

My family came to Glengarry about 1820 and I think the one or two rr dilemna may be just as simple as the transition between Gaelic to english. We use two rs but I have a Gaelic song written by my 4th great grandfather Donald and it has one r on it. Just a suggestion however ;)
Good luck with the hunting, I know there was a Sarah Morrison Hunter from near Glengarry and she passed away a few years ago, maybe she was a relation?

Cheers