In the comments, Yolanda posted a reply to my query.

Thanks! This is a Buchanan family that is a perfect 67-marker Y-DNA match to my family. So far we have not found the connection, but it looks like two of my cousins will be visiting County Tyrone this year, one in the summer and one in the fall.

The Andrew that Yolanda refers to is the uncle of the man who did the Y-DNA test. Andrew's father was John, and the Samuel Buchanan who lived nearby was his brother.

I believe their father is William, who is the only Buchanan listed in Kirlish in Griffith's valuation.
http://www.failteromhat.com/post1845.php
Griffiths Valuation of Ireland
Buchanan William           Kirlish       Longfield West           Tyrone
(partial)

I will definitely share Yolanda's suggestions with my cousins.

I am open to further suggestions too!

Yolanda's Irish research blog can be found at alandofpromise.wordpress.com