This John Brown could be a brother of Samuel Brown, born about 1801 and died 28 Jun 1869 in Derrylileagh townland, Tartaraghan, Armagh. Samuel is my GGG grandfather.
There was also a William Brown in Derrylileagh -- he could be another Brown sibling. At Griffith's Valuation in 1864, William Brown was living next door to Ann Simonton, who in 1866 became the second wife to Thomas Verner, my GG grandfather. Thomas Verner's first wife was Mary Brown. It seems likely that Thomas could have met his second wife, Ann Simonton, by virtue of her living next door to William Brown, a relative of Thomas's first wife Mary Brown.
All speculation, but pretty likely I think.
Susan Rogers, Grass Valley, California