amazing. My first time on this list and I might have found some "cousins".
My gggggrandmother was Margaret Allan, married in 1780 to William Slowan at Redburns, Kilwinning, Ayrshire. Could she be the Margaret Allan daughter of your Thomas Allan and Ann Colvin? According to IGI they had a Margaret, christened at Ardrossan on 25th May 1760? I'll check it out further at New Register House one of these days but would be interested in any info either of you has.