The song I noted above isn't really about Montrose. "Montrose Lyns", the song, is in Watson's 'Choice Collection', III, 1711, and the tune of that title, from the Blaikie MS of c 1692, is given in John Glen's 'Early Scottish Melodies'. If I remember correctly, Montrose died in 1643. There aren't many Scots songs of that date around, but I've seen a few scraps related to the Scots and their support of Charles I, of slightly later date. "Lesly's March" is probably the best known.