HI Char, the death are only on the civil record post 1864 see https://www.irishgenealogy.ie/en/ Click on civil records, I see a number of Owen Boyle deaths but none at the correct or aproximate age give the correct address and there were a lot of Boyles in Cooley north of Dundalk whereas the Boyle we are looking at is about 20 miles away. Deaths were haphazardly recorded prior to 1864 for Catholics and you can see here what is available by parish and year, again recoords for Togher parish have very early deaths but none post 1820. It is possible Beernards death cert in the US may contain information on his parents which would indiecate to us if we are on the correct track. I looked at 3 deaths per 1864, in hte 1840s and all were in Carlingford.
I have answered a number of queries on the Togher parish area in general and the 3 that stick with me are Carroll; Landy and Markey. I searched the transcribed inscriptions and found only a husband and wife Grogan in Dromin, no year given, in a large grave so appears to be pre 1900 but post 1880. Main name is McCann.
The Foster document was done in 1852 I think, I have a copy, Griffiths Valuation was done about 1854 here but the Foster document lists all in the house whereas GV only has the head of house and landlord if different.
If you look at the deaths in the site I sent you and find one given time I can probably get the inscription if listed there. I have looked at a lot of inscriptions locally on my records but no Boyles on them. Poorer people are unlikely to have a headstone.
The general opinion I formed from other queries is most emigration appears between 1846 and 1860.
If you do DNA it might assist if you have matches to the names mentioned in the locality, however having recently done my own it is not as clear cut as you might imagine and introduces so many new names as to be a bit overwhelming but interesting.
Regards
Pat