I had hoped to get some later details of Belfast street listings to narrow down dates for McGourans and Mallons, but haven't heard anything back yet so far - the more recent data can be less easy to access online.
Took a look at the locations mentioned and step back in time in case these have not been mentioned already : Saintfield is a town and civil parish, Carrickmannan townland is in Killinchy civil parish, Ballygowan townland is in Comber civil parish. Comber civil parish, which is to the north of and adjacent to both Saintfield and Killinchy civil parishes.
(post-town & civil parish) -
Saintfield RC parish covered Saintfield and Killinchy civil parishes and I think most of Comber civil parish would have been covered by Newtownards RC parish, but the boundaries may not have followed the civil parishes exactly.
Griffith's Valuation took place in 1863 for this area and shows a few Carson and Mullen entries in the various civil parishes :
Killinchy cp : Patrick, John, James & MaryMullen
James listed with a forge in Carrickmannan townlandSaintfield cp : James (x3), William (x2)
Comber cp : Robert, John, Thomas
John is listed with a house, forge and small plot of land (more like a garden), and located in Ballygowan townland - so poss. grand-father or uncle to Rose.
Comber cp : James, Samuel (x2)
Killinchy cp : Daniel, Margaret, Bernard, Henry
Saintfield cp : Jane