I can help you...what are the names of your Grumbles? I need to look back to around 1900 to find out so that may be grandparents or ggrands.
P. S. The Choctaws don't and didn't live on a "reservation" - they had a Nation in Indian Territory (now OK) which is the entire southeast part of the state. After 1907, when OK became a state, each Choctaw got an allotment of land and then the rest was sold / settled by non-Indians. The Choctaw Nation (OK) is still in the same place and their Nation is concurrent with the state in their original area.