I have kept working to search for and disinter interesting tracks of Scottish singers in the Ole Miss Goldstein Archive, with the kind permission of archivist Greg Johnson.
I have just added tracks of
Ray and Archie Fisher at an English festival in about 1971,
a distinctively Scots rendition of Old Timey song The Baldheaded End Of The Broom,
young Fetterangus sisters Elizabeth and Jane Stewart in 1960 singing beautifully, including the original that Ewan MacColl drew on for 'Come Aa Ye Fisher Lassies', and Elizabeth singing in Philadelphia in 1972.
And more.
I hope to get around to uploading Jean Redpath demonstrating various Scots accents to the Philadelphia Folklore Society. She includes quite an effective imitation of how Billy Connolly sang 'Salti-coates Goodeebyee'. Hear the tracks at https://goldsteinandscotland.com/listen-to-these-gems