That figure is according to Karp. In The Path to Power, the first installment of his massive biography The Years of Lyndon Johnson, Robert Caro puts Democratic losses in the House at 82 seats (p. 610). The World Almanac puts Democratic losses at 71 and Republican gains at 80, with "other" affiliations losing nine seats.

Robert A. Caro, The Path to Power (New York: Alfred A. Knopf, 1982).