What denomination church was the marriage for Allen - could a Church of Ireland/Anglican baptism fit ?
Might be worth checking out the that 1829 baptism to see if a father's occupation is mentioned. I would think an father of the child being Army captain (R.H. = ?) is something that might be mentioned on a record. If nothing else to eliminate this as it's the closest match showing up among records online..
I don't see a barracks in Kilalla at that time, but there could have been one somewhere nearby..