I don't know about your McGivern relations, but mine are GREAT!They're a bright, warm, hospitable and FUN group!A great sense of humor appears to be hereditary with one and all.
Now, do you have any idea when and where your ggrandfather James Thomas was born?My gggrandfather (Peter Andrew) left behind a number of siblings in Co. Armagh -- none named James Thomas; however, one brother was named Thomas and a number of the brothers had sons named Thomas -- but no James Thomas.Chances are your ggrandfather was from either Co. Armagh or Co. Down -- that's where the McGiverns have been concentrated for centuries.Fortunately, for research purposes it isn't a common name.Have you tried posting to any of the message boards for Counties Armagh and Down?
I have a cousin who has been to Counties Armagh and Down a number of times and he reports McGiverns still abound, particularly in the Newry area.However, the ones he has met do not appear to be too into their ancestors (unfortunately for folks like us!).
Gook luck in your search and let me know if there's anything I can do for you!