In her biography* of Sylvia Plath, Anne Stevenson refers to an unpublished letter of 13 June 1953, written by Plath to her mother, mentioning that the taxi in which some of the guest editors were travelling to the ballet became stuck in traffic.
According to the letter, a man approached the taxi and said, "Too many pretty girls for one taxi. I'm Art Ford, the disc jockey. Come in for a talk." Some of the guest-editors did get out and join him in a café, and spent some time with him in Greenwich Village later that evening.
We do not know, of course, to what extent (if any) the character of Lenny Shepherd is based on Art Ford!
*Bitter Fame: A Life of Sylvia Plath (Penguin, 1990) p. 41.
An interview with Art Ford: