MLA

Steinberg, Saul, 1914-1999. Gettysburg, PA. Box 445, folder 6082. undated. https://collections.library.yale.edu/catalog/33091953.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 445, folder 6082"])(undated)[Gettysburg, PA]. https://collections.library.yale.edu/catalog/33091953.