Sorry -- forgot to say that the Breton tune (for Twa Corbies) came from Glasgow schoolteacher Morris Blythman, who was taught it by Breton folk-singer Zaig Montjarret (with an acute accent on the e!). Morris recognised the 'rightness' of the match and it began to be sung around, and was also published in a weekly series of Scottish folksongs that Norman Buchan provided for the Weekly Scotsman newspaper in the late 50s/1960 or so. The songs in this column became the impetus for the eventual publication of Norman's "101 Scottish Songs".
To go off on a wee divert, both Norman and Morris were English teachers and had folk clubs in their respective schools (Rutherglen Academy and Allan Glen's), they were close friends and both shared their book and record libraries generously with interested youngsters. Ray and Archie were brought up just a couple of streets away from Norman's house, and were often round there looking for songs, and when Norman and his wife Janey began putting on concerts with visiting singers like Cisco Houston etc., Ray and Archie were often included on the bill. So, although it was a sizeable city, Glasgow's folk music community was close-linked.
Apologies for any thread drift.