I'm very late on this, but I found this thread while trying to research my family's old property. The place referred to in the perambulation is Castel-y-Bwlch. It is NOT the same place as Castle-a-Buff. I'm a first-generation American, myself, but I am familiar with the landmarks mentioned, after visiting Castel-y-Bwlch with my uncle on one of my visits. My dad used to play in the brook mentioned in the perambulation when he was a child.

Here are photos of Castel-y-Bwlch and property, taken from our visit.