I know nothing about the Missouri Reeves family, but suspect that the William M. Reeves of the First Indiana Cavalry isn't your man. The Indiana Adjutant General's report states his residence was Indianapolis. I can't find him as an enlisted man (Sergt., according to CWSS). Reeves was 2nd Lieut. of Company M; Companies L and M were 9-month draftees (though some officers came from other regiments) and didn't join the other eight companies of the First Indiana Cav until January, 1863, at Helena Arkansas. This William M. Reeves is also listed as a Captain in the 46th Rgt Colored Troops, which was the old First Arkansas Infantry, African Descent, which was formed at Helena in the spring of 1863. Though the Indiana Adjutant General's report states Reeves was mustered out with Company M (circa July 1863) he must have stayed in Helena while the First Arkansas A.D. was organized.