MLA
Stibbs, John H. Letter from John H. Stibbs (New Orleans, Louisiana) to Emory Professor Bell Wiley (Atlanta, Georgia) Regarding Programs and Documention of the Grand Army of the Republic, Military Order of the Loyal Legion of the United States, and Other Civil War Societies That John's Grandfather, John Howard Stibbs, Was Involved in after the War. 1973. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 23, Folder 30. https://digital.library.emory.edu/purl/641mgqnmnw-cor.
APA, 6th edition
Stibbs, J. H. (1973). Letter from John H. Stibbs (New Orleans, Louisiana) to Emory professor Bell Wiley (Atlanta, Georgia) regarding programs and documention of the Grand Army of the Republic, Military Order of the Loyal Legion of the United States, and other Civil War societies that John's grandfather, John Howard Stibbs, was involved in after the war (Box 23, Folder 30) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/641mgqnmnw-cor.
Chicago
Stibbs, John H. “Letter from John H. Stibbs (New Orleans, Louisiana) to Emory Professor Bell Wiley (Atlanta, Georgia) Regarding Programs and Documention of the Grand Army of the Republic, Military Order of the Loyal Legion of the United States, and Other Civil War Societies That John's Grandfather, John Howard Stibbs, Was Involved in after the War.” Letters (correspondence). Civil War Collection, 1973. Box 23, Folder 30. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/641mgqnmnw-cor.