He married Marrion McArthur 24 May 1755 at Callander. There is also another marriage 13 Jun 1755 at Port of Menteith to Maryion (sic) McArthur. Am confused about these two marriages ??
The registers of marriages are, strictly speaking, registers of proclamations or banns, and record the fact that the intending marriage was announced three times from the pulpit so that anyone who had a legitimate objection to the marriage could make it publicly known. The registers may also, but do not necessarily, record the date of the actual wedding ceremony.
If the couple resided in two different parishes, the banns had to be called in both parishes, so you get a double record of a single marriage.
So what this tells you is that at the time of their marriage in 1755 one of the couple lived in the parish of Callander and the other in the parish of Port of Menteith. The original record normally makes it clear which way round it was.
The IGI, Ancestry, GenesReunited, MyHeritage, Geni etc etc can only give correct information if the information exists in the originals. These sites are not repositories of original material, and they are not an alternative to Scotland's People, though some of them are very useful finding aids. There is a very small number of registers from the mid-18th century that for one reason or another are not in SP, but they are very few. If there is nothing on SP, then you need to be *very* suspicious of any dates that crop up on sites like those; don't believe them until you have traced and viewed the original source document.