MLA
Best, James W. Letter from James W. Best (Camp near Dalton, Georgia) to W. R. Enecks (Egypt, Georgia) - January 25, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 3, Folder 20. https://digital.library.emory.edu/purl/726xwdbsx8-cor.
APA, 6th edition
Best, J. W. (1864). Letter from James W. Best (camp near Dalton, Georgia) to W. R. Enecks (Egypt, Georgia) - January 25, 1864 (Box 3, Folder 20) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/726xwdbsx8-cor.
Chicago
Best, James W. “Letter from James W. Best (Camp near Dalton, Georgia) to W. R. Enecks (Egypt, Georgia) - January 25, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 3, Folder 20. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/726xwdbsx8-cor.