Two things not mentioned. He had a long and often vituperative discussion with Hamish Henderson in the pages of the Scotsman about the nature of Scots Traditional Music and in particular the big ballads. Some of this is related in the book "The Armstrong Nose" which covers Henderson´s correspondence.
He took his pseudonym from a Lallans poet. (Plenty about these on the internet- google for it if you are interested) The connection with MacColl is that he may have done the same (almost) for there is one called EVan MacColl.