I think you need to be very, very careful here about jumping to conclusions.
Yes, Lafferty will probably have may spelling variations as most writing was done phoentically by how a word sounded.
Killymuck Glebe (glebe meaning lands belonging to the Established Church i.e. Church of Ireland) is the name of a townland in the civil parish of Tamlaght O'Crilly. In the countryside we only got road names about 40 years ago- previously the only 'address' would be the townland.
Griffith's valuation will list names of occupier (head of household) in a townland but just because you found a James Lafferty does not mean he's the one you are looking for and even if the family did live in that townland the James Lafferty listed could be your James' uncle, grandfather, cousin, etc.).