MLA

Gascoyne, David, 1916-2001. Munton, Alan. Box 9, folder 126. 1999. https://collections.library.yale.edu/catalog/2055489.

APA, 6th edition

Gascoyne, David, 1916-2001. (["Box 9, folder 126"])(1999)[Munton, Alan]. https://collections.library.yale.edu/catalog/2055489.