William C. Gullick is not included in my research of "Union County Confederate Burials"
http://www.rootsweb.ancestry.com/~mscivilw/unioncovets.htm which I used several references including "Mississippi Confederate Graves Registry". It isn't 100% complete as I found one soldier (a musician) yesterday while looking for William, I've spent the last couple of days looking for him. I found some of his children but not him.
It is kind of weird, I went through the entire 1880 and 1900 Union County census, he was in neither....though some of the family moved to OK then moved back. As most of the likely children I found were born around 1890, I imagine he was on the burned 1890 census.
So far, like Mr. Gullick, I have been able to find no record of him excepting military.