ABC shook up its news magazine division last week, appointing Victor Neufeld, long-time executive producer of the '20/20'magazine franchise, senior executive producer of the ABC News magazines. Three new executive producers will have day-to-day responsibility for the magazines: Downtown (airing Mondays), Prime Time Thursday and 20/20 (airing Fridays). David Sloan will helm 20/20. He has produced John Stossel's ABC News Specials. The two other executive producers are to be named shortly. One rumored possibility for the investigative-oriented Prime Time Thursday: David Doss, who recently ended a five-year run producing NBC Nightly News. Doss couldn't be reached by deadline for comment, although ABC insiders strongly downplayed the rumor. Neufeld will continue to report to ABC News Vice President Phyllis McGrady.