The Roster of Confederate Soldiers, 1861-1865, shows it as you gave it:

Howard, Willis GA 12th (Wright's) Cav. (St.Guard) Stapleton's Co. 1st Lt.

12th GA Cavalry Regiment, State Guard organized in late 1863 & mustered out 2/4/64

Roster also shows:

Howard, Willis S. GA 34th Inf. Co.B