Kinross TMSA festival- I was there & well remember Davie Glen & his big beard & diddling- Paddy Tunney was another fine exponent. Davie was also often called on for his expertise in finding daft hikers lost in the hills.
As for all this pseudo-historical folklore about diddling FFS we all do it when we hear a decent tune, pop, folk, Debussy, Abba or whoever- it's not a study worthy of an Masters degree.
    The natural successor to the Kinross diddling event is still held in early September at the Kirriemuir TMSA festival, north of Dundee. I entered once & became the second best diddler in Scotland for a year -
a doubtful honour, maybe, but I treasure my certificate.
    Talking to Jimmy Hutchison the great singer from South Uist at the time, he told me that years before, he & the then unknown Irish singer Christy Moore would have a private diddling competition where the winner was the one who could insert the word 'scrotum' most times-

nb this was NOT authorised by the TMSA- Jimmy was one of the founders...