MLA
McCoy, Oliver. Letter from Oliver McCoy (Gerard, Kansas) to Carrie King[?] (Waco, Texas) - August 8, 1908 (Photocopy). 1908. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 19, Folder 35. https://digital.library.emory.edu/purl/6386hdr90j-cor.
APA, 6th edition
McCoy, O. (1908). Letter from Oliver McCoy (Gerard, Kansas) to Carrie King[?] (Waco, Texas) - August 8, 1908 (photocopy) (Box 19, Folder 35) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6386hdr90j-cor.
Chicago
McCoy, Oliver. “Letter from Oliver McCoy (Gerard, Kansas) to Carrie King[?] (Waco, Texas) - August 8, 1908 (Photocopy).” Letters (correspondence). Civil War Collection, 1908. Box 19, Folder 35. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6386hdr90j-cor.