Hi Rhiannon. The townland is Kilbeg, i.e. Little Church. However, the stone is in a field (there is another bullaun stone with one basin in the same field but I've never found it) at least a quarter of a mile away from any church. The basins on this one are notable for their width, one nearly a foot wide. A thing of beauty.
Rhiannon, I don't see why either of your ideas couldn't be correct. I've seen some different instances that would fit both of them. I've also seen many other instances that would suit quite a few other theories.
This single-basin one http://www.themodernantiquarian.com/site/15839/ballymorin.html that I visited recently had a real ancient, pre-christian feel to it, but there it was in a churchyard - yet pushed to one side and without any evidence that it was ever used as a holy water font. Then again, there's a holy water font down in the church in Rathfarnham that looks like a bullaun stone that's been re-worked to fit on top af a small pedestal.
I'm guessing (it's all guesswork, innit?) that it was yet another instance of those nasty old christians knowing a good thing when they saw it and incorporating bullauns into their own tradition. I seem to remember that there was a bullaun book due out soon. It will make interesting reading.