Did the Corries say where they got that one?  On the face of it, it looks like a slightly modernised and drastically shortened set, with Carlisle substituted for Stirling, of the text collected by Burns, who added some verses of his own before contributing to the Scots Musical Museum.  It retains the references to swords bent in the middle which appears to be a corruption of the more usual pointed with the metal.

Roger the Skiffler has pointed out in the second thread that Sarah has started on this song that reiver or reaver is a perfectly good reading for one of the problematic words, as the Graemes or Grahams were a well-known family of bandits.  I don't know about the other word; carrion might I suppose be a vague possibility.  Neither term appears in any of the traditional sets I've seen; great though my affection for him is, Robin Williamson has never been renowned for faithfulness to his sources.  He is perfectly capable of having made that bit up himself.

There are two sets in the DT; HUGHIE GRAME, which Susanne linked to above, is taken from a record by Ewan MacColl, and appears to be a cut-down version of Child's E text (Buchan's MSS) and HUGHIE GRAHAM,  which is Child's B text; the one from Burns.