I think I have a loose connection with all three of you. I'll explain :-
1. Stephen - I have been writing to John Glackin of McCrae Park in Drumquin for the last 5 years and I'd hazzard a guess that he's your Grand-father? He's a very nice guy and I will be dropping in to see him this summer as I pass through on my caravan touring holiday of Ireland.
2. Chris - My branch of the Glackin family originated in your area - Coalisland in fact. My Great-grandfather John Glackin left there something like 130 years ago married a Coalisland girl (Catherine McLernon) in Motherwell and raised a family. I have a record of all his descendents in Scotland, but nothing on any of the family he left behind. I would guess that some went to America and some stayed in the area, I hope to find out this summer.
3. Mark - I have an index of every Glackin who was born, married or died in Scotland from the time that records began in 1855, up to date (but no Garry Glackin). If your ancestors lived in Glasgow, I may be able to give you some information if you like - drop me an e-mail. I've got to say though, that it's my believe, that all the Scottish Glackins have Irish Roots. So maybe your Grand-father worked in Glasgow at some time.