Using Ancestry's database, Georgia, Returns of Qualified Voters & Reconstruction Oath Books, 1867-1869: https://www.ancestry.com/search/collections/ga1867votersoath...
, take a look at Clem Long in Gwinnett Co. GA [Gwinnett Co. adjoins Forsyth Co. GA]. In the Voters section, he's listed as "Col" The index lists him as Clen Long in the Oath section; he signed with an X.
I realize this doesn't really answer any of your questions, but it is a listing before 1870.
If you go to the GA page on Ancestry, you might try the GA Tax Digests. I have some other ideas.