There is a Longford Co. DNA family Project at www.familytreedna
(They do the testing for National Geographic's Geno Project)
There are a lot of Family Projects on the go already at Family Tree Dna. More people are joining all the time. Take some of the guess work out of your search and link up genetically with other Johnstone People. I am only a member of the family projects. The only gain I get if people join up, is more relatives, and a better understanding of who I and my ancestors really were.