If our sensitive guest asked for some information and didn't come back for two years to see if any was given, she probably won't be back to see what we might say about her now, but I'd like to thank her for refreshing this thread, which I'd never seen.
This is one of my favorite songs, too. I got it from the singing of Sinead Cahir and also of Cathal McConnell. Neither of them use the verse in question, and neither does Sean O'Boyle include it in his book, The Irish Song Tradition. The words of the four verses in O'Boyle's book are essentially the same as what ard mhacha posted above, but there are many little differences. If I can get it together to find the time, I'll post O'Boyle's version.
Concerning the culture of origin, one suggestive line has not been pointed out: "And let them all say what they will, and let them reel and rally-o." O'Boyle suggests this might refer to opposition to the marriage, and , considering the location, it might be sectarian opposition. In which case there might be a Catholic influence in the words. Of course, that's a lot of maybes and mights to build an argument on. An interesting point anyway. Yeah, yeah—interesting but not persuasive. Oh well. It's a beautiful song, regardless—and one of the few love songs not about lost love!