I am not aware of any book specifically written about the 9th Battalion Mississippi Sharpshooters.
There was a Zachariah Lofton listed among the members of the 7th Mississippi Infantry, according to the National Park Service's Soldiers and Sailor's website at http://www.itd.nps.gov/cwss/soldiers.htm. His alternate name is shown as Zack Loften. This may well be your g.g. grandfather.
There is also a website devoted to 9th Battalion Mississippi Sharpshooters at the following website: