Jean Shepherd, WOR Radio personality, award - winning novelist, only three-time winner of the Playboy Magazine Humor Satire Award, has been awarded a Rockefeller Foundation grant as Artist In Television. Shepherd will be a Rockefeller artist at WGBH Television in Boston, Mass. WGBH is part of the Harvard-Lowell network, and will originate and produce Mr. Shepherd's shows. Shepherd's show will be an experiment in existential television. Entitled "Rear Bumper", it will be carried on WGBH (Channel 2) beginning in October at a date to be announced. "Rear Bumper" will be directed by Fred Barzyk of WGBH-TV. Under the auspices of the Rockefeller Foundation and the Harvard-Lowell network, Jean Shepherd will be given the opportunity to bring his unique creative humor to the television medium.