Jay, there is a WWI draft registration for a John Oliver Hefner in Atlanta, Fulton County, Georgia. It states his age was 30 and he was born September 18, 1886 in Gordon County, Georgia. He was an "automobile machinist" and was married. Is this your line?
My 2nd great grandfather, George W. Hefner was married in Gordon County, Georgia 26 Oct 1865 to Savilla Holcombe.
I would strongly suggest you DNA test as you could be related to this family. See my line and H-8 in the link below.