MLA

Pound, Ezra, 1885-1972. Letters. Box 63, folder 2766. 1961. https://collections.library.yale.edu/catalog/32161215.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 63, folder 2766"])(1961)[Letters]. https://collections.library.yale.edu/catalog/32161215.