The LeFlore County USGenWeb site has a map showing exactly where the Kully Chaha area was located. Click on this address:http://www.rootsweb.com/~okgenweb/twpmaps/leflore.html
The mention of Sebastian County AR may have been to tell someone where he received his mail, but it was not part of the Choctaw Nation or even Indian Territory.
As for "Indian blood"; if he was Indian, that will be shown on the 1900 U.S. census - what tribe, the degree of Indian and white blood of each parent. The 1900 Indian Territory census does (thankfully!) have a Soundex to help you locate the family and which roll of census film to go to. These records may be rented (less than $5.00) and brought into your own public or LDS library on microfilm. To the best of my knowledge- they are not "on-line".