My gggrandfather Ewen McDonald had the alias MacIsaac. He was born in Glengarry, Kilmonivaig ,Inverness, Scotland. He was born around 1780 ,the son of Alexander and Mary[ nee McMillan.] He was a shopkeeper/Crofter in Fort Augustus. His son Donald was my ggrandfather who left Scotland around 1863 for Australia.
You mentioned your Donald came from Fort Augustus. What time period did he live there?