C.A., do you know if he served Confederate or Union? There are several William Wilburns. There is one in the 2nd Arkansas Cav USA, one in the 3rd AR CAV, USA, one listed in the 3rd AR Cav
USA. Northern Arkansas, especially the Harrison area, had many of its men to join union units. It was truly a house divided, brother against brother.
The Original Arkansas Geneaology Hompepage (Edward Gerdes page) has rosters and when available, history of units. The National Park Civil war Soldier's an Sailor's System, usually has unit histories available.