I wonder if those Witten's in Humboldt County, Kansas, were part of the uncle's family? It's not a common name.
I have those Saline County Witten boys in my database. The family paid a heavy, heavy price in the Civil War.
BTW, my records show First Sergeant Coke Witten, Co. F, 1st Arkansas Mounted Rifles, killed in action at Dug Gap, Georgia, on May 8, 1864. Does that jibe with your records? The reason I ask is that Arkansas casualty reports during the four-month Atlanta campaign are kind of jumbled up. Most are based on the August 31, 1864, muster rolls, and thus attributed in part to memory.