Thanks for that info.
If you look at the "Crossmaglen Catholic church" in pictures on, for example, Armagh genealogy sites, it's the same one as you see on the Armagh Diocese site and which is called St Patrick's. It was built in 1835. Rather a monstrous building and enormous for the village of the time, I would say.
At least it would make it more likely that all religious ceremonies were performed there. I mean, if it were just the "chapel" quoted in Lewis's Topo. then you might go further afield for your wedding (maybe).
Having said that, why can't I find the marriage I'm looking for???