I think you are correct about there being more than one Alexander Mann. The one in my tree definitely originated from Culloden (b.1767), and his wife was Jane Dallas. There is a son, Donald listed in his family in the 1841 census, at Culloden Moor. There was another Alexander Mann at Brae of Cantray, Croy (b.c1807)who was also married to a Jane Dallas. He was a mason, according to the 1841 and 1851 census. Unfortunately, the same Christian names keep cropping up in both families.