My gggrandfather was the 1st Lt of Co B, 8th MO Infantry (Mussers) Battalion so I know a little about the unit. It was formed mostly from exchanged prisoners from Alton, IL during a large exchange around Sept 62. William McWaters had been a member of Peyton's Regiment (presumably 3rd Cavalry Regiment, 8th Division, MSG) and was captured 5 Apr 62 in Bates County, AR and sent to Alton, IL from where he was exchanged and ended up at Camp Horsehead, AR where he joined the 8th Bn. Peyton's Regiment in the 8th Division of the MSG was formed mostly in Lafayette County, MO.
Hope this helps,