This hump-chariot hall of fame not only features fine reproductions of a '50 Ford tudor, a '53 Cadillac coupe, and a '56 Chevy hardtop but is narrated by the swingingest host of them all, Ed McMahon. It's fun to imagine him working behind the brake counter at Pep Boys the day Mrs. O'Doylie stopped by and said, ''Eddie, come out here and look under my hood.'' The rest of what happened in her '56 Lincoln coupe is sure to get your engine humming. As is Ed's va-va-vooming description of bedding all three Lamberta sisters in the back of his '50 Studebaker pickup. You might just discover the true meaning of ''Heeeere's Johnny!''