In the February 1976 issue of Word Ways, Robert Cass Keller called for readers to construct an interlocking rectangle of the 33 different surnames of U.S. Presidents (keeping Van Buren as two separate words). Although the following 17-by-31 rectangle is a fairly compact one, it may be possible to find another with slightly smaller dimensions.
"A Presidential Rectangle,"
Word Ways: Vol. 9
, Article 4.
Available at: http://digitalcommons.butler.edu/wordways/vol9/iss2/4