This caught my attention because he's buried in Oklahoma. I did some searching online and found the below info.

The 1910 US Census for Midland Township, Pontotoc County, OK shows James M. Downing, age 66, born Missouri, Confederate veteran, and spouse Martha J. Downing, age 65, born Missouri, married 44 years.

The 1920 US Census shows James age 77 and Martha age 75.

The 1860 US Census for Jim Henry Township, Miller County MO shows James M. Downing, age 15, born Missouri.

A family tree record on Ancestry.com shows him as married to Martha Jane Jackson in Morgan County MO in 1866. It also says he was a Baptist minister.

Findagrave.com for Midland Cemetery shows:
Birth: unknown
Death: 1915
Civil War Veteran, Pvt. Co. A, 9th MO SS-CSA
Husband of Martha J. Downing
Burial: Midland Cemetery, Vanoss, Pontotoc County, Oklahoma, USA

Note that the death date on Findagrave is incorrect because he is on the 1920 US Census.

Fold3.com shows James Downing as private in Company A, 9th Battalion MO Sharp Shooters (Pindall's Battalion). He enlisted Aug. 15, 1862 at West Plains and served as cavalry prior to Nov. 9th -- I presume in Capt. Reavis' (Reaves) Company MO Cavalry which be came part of the 9th Bttn MO SS as of Nov. 11, 1862. An undated record says he was left behind sick between Ft Smith (AR) and Lewisburgh(?). Another record says he deserted Dec. 27, 1862 from C. Mazard which is likely Camp Massard, Massard Prairie being a large area southeast of "old" Ft Smith. He is also listed on a POW record as surrendered with the Trans-Miss Dept May 26, 1865 and paroled at Shreveport June 7, 1865. His residence is given as Jefferson City.