I don't know if this helps in any way, but I played at the Shrewsbury Festival in 1987. I was playing in Wild Edric's Band at the time and we played a ceilidh on the Friday night (3 july, 1987). If it helps jog your memory, Gas Mark 5 and Eddie Upton did the Saturday night ceilidh. I have these details down in an old diary, but have no more than that. Jim Mageean may well have been on the bill that year, but as he was the son-in-law of the festival committee members he was often around and so I couldn't specifically say.