Mary Gregg gave some information in 2006 which said Robert L. Cochran Sr. married Jincy Bohanan after 1850 in Indian Territory, son of William Cochran and Elizabeth Owen. He was born August 30, 1815 in Oglethorpe County Georgia and died in 1864. She married William Lewis Cochran November 22, 1865 in Pickens county Chickasaw Nation, I.T. son of Augustus Cochran and Frances Bailey. He was born Jan. 11, 1834 in Fayette County Tennessee.
I haven't studied all the dawes rolls but William and Jincy's daughter Eugenie I think was listed as 1/16. So I think the Choctaw Blood was coming from Jincy and not William or there would have been more quantum blood listed.
I do not know about Robert Cochran but he is listed on a Choctaw Census card as a parent with Delete Brashears. I don't have the original that should tell you on there if he was on a Chickasaw or Choctaw Roll therefore telling you if he is Indian or not. Accessgenealogy.com has a search engine for the Dawes rolls and some other censuses for free.
I am still trying to figure it all out since this connection with Jincy Bohanan to the Cochrans. Thanks for the map also.