He would have been initially buried at Curtis Plantation about two miles from Fort Pemberton. The Saint Lewis left and then was turned back until April 12.
There might be more information available at the city of Greenwood.
There were about a dozen buried from the 28th alone from a force of about 4000.
By Army regulations the graves would have been marked with wooden posts many often gone (used for firewood?) by war's end and their removal to National Cemeteries. There is a very good chance of finding where the remains were taken by looking for others that would have been buried in the same place.