Last week's balmy spring weather found workers installing a plaque outside MSEL to honor its benefactors: R. Champlin and Debbie Sheridan, who in 1991 endowed the library director's position and, in 1994, made a $20 million commitment to nearly double the library's endowment and support its planned renovations. In February the Eisenhower Library and its collections were rededicated in their names.