Hello
I'm quite keen to get in touch. My gg grandfather was another John McCarthy, master cooper of Fair Lane, Cork city, his father was Thomas, also a master cooper. John was born c 1824. It is possible the two Johns were related. My John was a widower on 20th Nov 1855 when he married my gg grandmother, Elizabeth Roche, they were married in St Lukes, a Church of Ireland church near Fair Lane. It's possible John was Catholic - Elizabeth was definitely protestant. I was thinking your John may have been a cousin or some other relative given the location, name and occupation coincide. It is also possible your John was a son from my John's first marriage. Have you had a dna text? It could be very interesting.
Cheers
Sue McCarthy
Sydney, Australia