Sept. 14, 1961 - Former Vice President Richard M. Nixon challenged former President Harry S. Truman today to a piano-playing contest. "Since I've had time to practice," Mr. Nixon said, "I think I can play 'The Missouri Waltz' better than he does, but I'll have to admit he is better at Tchaikovsky." Mr. Nixon was in Denver to address the American Legion's national convention. Mr. Truman addressed the convention today. "If we can't beat them at the polls," Mr. Nixon declared, "we can beat them at the piano."