RON PALILLO . . . who played high school student Arnold Horshack on the '70s sitcom "Welcome Back Kotter". . . died yesterday morning of a heart attack. He was 63. "Kotter" ran from 1975 to 1979 and as you probably know, it launched the career of JOHN TRAVOLTA. Here's a clip of "The Great Debate". See if you recognize a well known hollywood actor in this besides Travolta.