It's on Steeleye's "Live at Last" album.I've got a book about Montrose called "The Proud Servant: The Story of Montrose", which is not a bad read although a bit romanticized. Can't seem to lay my hands on it at the moment so I don't know the author.
Thanks for the informative posting at the top, Reiver, which would have been a great help to have when I read the book--couldn't quite figure out all the switches in allegiances.
The Covenanters, "true Calvinists" are still around, by the way, known mostly as Reformed Presbyterians but they also call themselves the Church of the Covenant. Some are friends of mine, and I was a little surprised when one--a guitar student of mine--explained that the regular Presbyterian Church was too liberal for their liking!
Bill