Don't know if this will help. Duke W. Simpson had sons Nathan and Benjamin F. Simpson (Half-brothers). Nathan was a childhood friend of Upton Hays and Upton's son, John Nathan Hays was named after him. The family is listed in the 1850 Kaw Tsp., Jackson Co., MO Census.
But this Benjamin F. Simpson seems to have survived the Civil War because I found a man by that name in the 1880 Westport, Jackson Co., Census living with his brother George E. Simpson.
I think this is Nathan but haven't checked it out. It appears that Nathan went to Nebraska after the CW.
N.R. Simpson (First_Last)
Regiment Name 3 Battalion Missouri Cavalry.
Side Confederate
Company D
Soldier's Rank_In Private
Soldier's Rank_Out Private
Alternate Name Nathan K./Simpson
Notes
Film Number M380 roll 13