Sir- All the locatable Federal burials at the Ft. Pickering site were disenterred and moved to the National Cemetary in 1865. I am a Memphian and am unfamiliar with a Mississippi Riverbank cemetary in the area of Ft. Pickering( now part of the City of Memphis). The first Thousand or so burials at the NC were Illinois troops moved from Ft. Pickering. I found no identified Ohio casuality being reburied at the NC but did find five other members of the 70th Ohio.
J.C. Black-dod5/13/65-Co. K, plot# 4729
Oliver Grey -6/22/62 ,"F", plot #4712-body moved from Moscow, TN
H. Cornelius-7/5/63, plot #4713-body moved from Moscow
Michael Joice-12/28/63,"H",plot# 4695
Daniel Liter-10/6/63, "B", plot# 4965
J.L. Swisher-1/30/63, "F", plot# 4887 body moved from LaGrange

It appears poor records were kept of Ohio burials at Pickering, so your guy is most likely undr an unknown stone in the Ohio section of the Cemetary.