A possible source for Georgia name changes is "Georgia Black Book: Morbid, Macabre and Disgusting Records of Genealogical Value" by Robert S. Davis. It seems to be out of print but I've seen in in several genealogical libraries.
If I remember correctly, and I'm not going to guarantee that, the book included some name changes. There may also have been prison records in the book.
Hmm... if he went to prison there should be a record of that. You would probably qualify for the International Blacksheep Society of Genealogists http://www.ibssg.org/blacksheep/
. They may be able to offer some more ideas on where to look.
Did you find your grandfather's Death Certificate? What are his parents names on that?
Have you found him with his parents on any census? Or are you stuck because you don't really know his first name?
The SSDI is a good place to begin a search for recent deaths, but not everyone appears in the SSDI. I'm not sure of the date their records begin, but I think it was sometime in the 1960's.