Yesterday’s song about Philadelphia sent me back there today. The eight-track tape of the “Rocky II” soundtrack spent considerable time in my car in 1979, and in my bedroom, where behind closed doors I did push-ups and sit-ups to Bill Conti’s “Gonna Fly Now” and “Overture,” hoping to build my 16-year-old muscles in a way that would make Sly proud. Besides getting chills today at precisely the same moments in the score that produced chills 36 years ago, the nicest surprise in revisiting this soundtrack was this tune — sung in the movie by some rough kids around a trash-can fire on a Philly street corner after Rocky and Adrienne got engaged. This defines what I consider the classic Philadelphia sound. Interestingly, the soundtrack credits Bill Conti, who did the entire score. But a quick search turns up that it’s performed by the acapella group Valentine, fronted by Sylvester’s brother, Frank Stallone.