Marguerite Cullman, who learned to pick Broadway winners as a writer for Stage magazine and helped finance the original productions of “Oklahoma!” “South Pacific,” “Death of a Salesman” and “A Streetcar Named Desire,” died July 25 in New York. She was 94.One of her earliest jobs in the theater was to attend vaudeville performances to see if any jokes had been stolen from the gag writers who employed her. She later worked as a copy editor for the McNaught newspaper syndicate and wrote for the New York Times magazine and the New Yorker. At Stage magazine, she chose the monthly’s covers. Cullman wrote “Occupation Angel” in 1962 about her theater experiences and “Ninety Dozen Glasses” in 1960 about her travels.