Marion Wilson O'Bar did indeed serve in the Provisional Army of the Confederate States as a member of Capt. John Francis Erwin's Co. I, 33rd Arkansas Infantry. Captain Erwin's company was recruited in Montgomery County, Arkansas. Marion W. O'Bar enlisted at Caddo Gap, Arkansas, on June 24, 1862, by Capt. J. F. Erwin, for three years or the war; age 29; and was mustered into service with his regiment at Camp Hindman, Camden, Arkansas, on July 3, 1862. He was reported absent sick on the October 31, 1862, and August 31, 1863, muster rolls. The August 31, 1863, muster roll includes a remark that he was left sick in a hospital at Monroe, Louisiana, on August 4, 1863, by order of Surgeon Williams. He doesn't appear on any subsequent muster rolls, and there is no indication of when or where he died. The letter you found is new information. William Cox, the writer of the letter, was also a member of Captain Erwin's company.