This can't be the William Buchanan I'm looking for. His son James was born in 1845 so it would have been very unlikely that William would have fathered him at age 12.
The only things that I know for certain about William Buchanan is that he built a house at Corcreevy outside of Fivemiletown for his sons. It was a duplex that shared a common wall. James and his wife Sarah (Quinn) Buchanan lived in it until they outgrew it and moved to Gortmore on the other side of Fivemiletown. When Sarah died in 1882 James, along with his sister Mary, took all of his children and moved to the US. The information that I have is as Jame's kids remembered it.