MLA

Ford, Charles Henri, 1908-2002. Kirstein, Lincoln. Box 1, folder 96. n.y. Mar 19. https://collections.library.yale.edu/catalog/17124854.

APA, 6th edition

Ford, Charles Henri, 1908-2002. (["Box 1, folder 96"])(n.y. Mar 19)[Kirstein, Lincoln]. https://collections.library.yale.edu/catalog/17124854.