It's been a while since you posted this, did you get anywhere? I have a bunch of Dallas/Dollas & Gun/Gunn connections in Latheron and elsewhere in Caithness.
I can't find an Alexander born 1729 in Latheron or any time between 1724 and 1734 anywhere in Caithness. There is one born that year in Croy and Dalross and two others born 1733 and 1734 in Cawdor and Duffus respectively.
You can send me a private message if you need help researching these names in Caithness.