Thank you, all.
Yes, shanreagh, that's the family. (There are more sources on ancestry.com.) And yes, kiltaglassan, that death record is his. (There is also a death notice in the Belfast News-Letter, which led to finding his grave; thanks, Elwyn Soutter.) I can't find your 1866 death, rathmore; and anyway, how would it help? Clearly a different John McDowell.
The naming pattern is interesting. I'm pretty sure of those children. The birth dates for the sons are extrapolated from their declared ages at the 1901 and 1911 censuses; for the daughters from death dates and ages given on John's gravestone. For what it's worth, the second known son, Henry McLorinan McDowell, was named for his mother's father, as per the pattern. But it was Henry McLorinan McD's first known son, Samuel McMillan McDowell, who was named for his mother's father; second son, John, perhaps for his father's father; and then third son, another Henry McLorinan, for his father. So first and second in the pattern are flipped.
I had seen something like that pattern on irelandxo.com, and wondered about Thomas as the name of John's father, but haven't come up with a suitable candidate.
Younger son was just an ignorant guess, aghadowey; it's interesting that it could just as well be elder sons who made their living in the town. What I suppose goes on being likely is that John's parents were rural, though no doubt they may have already been townspeople. All I really meant is that the range of possible locations is quite extensive.
