It appears that the local UDC and SCV folks ordered these original stones and may have retained those records.
Gordon Cotton may have been involved as well as Edwin Bearss
In 1977, there were fewer than 50 headstones erected in the area. When the United Daughters of the Confederacy and the Jackson camp of the Sons of Confederate Veterans ordered and put in place about 1600 stones with names based on the Sexton's list.
http://freepages.history.rootsweb.ancestry.com/~taleese/soldiers_rest_vicksburg/history_of_soldiers_rest_1.htm
You got me pegged. Although, I was never involved with Grand Gulf, all my time was spent on PWRs.
My involvement is with the 43rd Tennessee who had 41 men on that 1998 list of 77 Jeff Giambrone found.
Have you checked the Historians office files at the National Park?