John Shannon seems to have died 1916 at the workhouse. He is buried in Glasnevin (address 12 Coombe gives a positive) The death record gives his birth year as 1867, so the only possible corresponding birth I can see is:
John Shannon
1866
Dublin South
Vol: 12
Pg: 649
The grave in Glasnevin is an extended one, so if you haven't gotten that record yet it would be worth getting the lot to see if parents are there as well.