Broadway general manager and producer R. Tyler Gatchell Jr., 50, died July 1. The cause of death was a heart attack, according to his longtime companion, Mark Shannon.Composer Andrew Lloyd Webber has dedicated his new production, “Sunset Blvd., ” to Gatchell’s memory. Gatchell and his partner Peter Neufeld founded the theatrical general management/producing firm Gatchell & Neufeld Ltd. in l969. Their office has been involved with more than 100 productions on Broadway, off-Broadway, nationally and internationally. Their association with Lloyd Webber dates back to the Broadway debut of “Jesus Christ Superstar” in l971. Since then they have been exec producers of “Evita,”"Cats,”"Song and Dance,”"Starlight Express,”"Aspects of Love” and the current “Joseph and the Amazing Technicolor Dreamcoat” and “Sunset Blvd.” Gatchell and Neufeld are currently represented on Broadway and in Los Angeles by “Crazy for You,” and off-Broadway’s upcoming “Annie Warbucks.” Among their many other productions are “No, No, Nanette,”"Sgt. Pepper’s Lonely Hearts Club Band on the Road,” the original “Annie,”"Sweeney Todd, “”Talley’s Folly,”"March of the Falsettos,”"Hurlyburly,”"Chess,”"Shirley Valentine” and “Lettice and Lovage.” Gatchell is survived by his father, Tyler Gatchell; mother, Patricia Leadley; two brothers and two sisters. Visitors will be received today at the Frank Campbell Funeral Chapel, l076 Madison Avenue, from 5-9 p.m. A funeral mass will be held Wednesday at 5 p.m. at the Church of St. Mary the Virgin, 145 West 46th St. A memorial service will be held in a Broadway theatre at a date to be announced. In lieu of flowers, family suggests contributions to the Professional Children’s School, 132 W. 60th Street, NYC 10023; The American Boychoir, Lambert Drive, Princeton, N.J. 08540; or Broadway Cares/Equity Fights AIDS, 165 West 46 th Street, New York 10036.