We happened upon this photo in the LIFE magazine archives. The caption reads: "Construction in NYC: land being cleared for 20 story building in East 60s — still occupied brownstone is soon to go." (It was still occupied!)
The photo was taken in 1959, and the brownstone was located at 215 East 68th Street, between 2nd and 3rd Avenues. Across the street where the numbers were even, there were 16 brownstones that got to stay—the NY Times once pointed out that they were "built as a piece in 1881 [by] developer John D. Crimmins—'No more than six of them will look alike, and no monotony will spoil the aspect of this new row of houses.'"
While those have survived (to this day), back on the north side the brownstones were being leveled for a new development that features around 600 rental units.
Update: In 2014, we revisited this post — find more info on this photo here.