There's a small chance that the baptism records might contain something useful.
I had a quick look for Kirk Session records. The ones for Saddell don't seem to have survived, but there are some records of Skipness
quoad sacra*. They are mostly accounts, recording how much money was collected each Sabbath and the names of the poor of the parish who received money, but there is a mention of Duncan Taylor in the sederunt on 21 December 1784, followed by his signature 'Dun Taylor' at the foot of the page. Is this your Duncan, or possibly his father, I wonder?
*
quoad sacra is Latin and means something like 'relating to sacred matters'. Parishes were not used only as religious units, but also for civil purposes
quoad civilia.
Sometimes there might be a significant population in a place in the parish too far from the parish kirk for most people to attend regularly, and the Church might then decide to disjoin part of the parish and erect it into a parish
quoad sacra (sometimes abbreviated to
q.s.) The religious division did not affect any civil use being made of the parish, which remained undivided
quoad civilia.
Skipness is about 20 miles from Saddell, but the parish kirks were at Claonaig and Carradale, which are only about 13 miles apart. Still too far for all but the most devout parishioners to walk both ways on a winter Sunday, so it's not surprising that there was a
quoad sacra division.
You can read a contemporary (1794) report about the parish from the Old Statistical Accounts at
https://stataccscot.edina.ac.uk/static/statacc/dist/parish/Argyle/Saddell%20and%20Skipness