THANK GOD! The score couldn't be played any other way.
They probably did away with one or both viola parts written for the 2 viola players who came to the theater who Bernstein didn't think were good enough, so he wrote easy parts for them.
"If there was a Mount Rushmore for Broadway scores, "West Side Story" would be front and center. It snaps, it crackles it pops! It surges with a roar, its energy and sheer life undiminished by the years" - NYPost reviewer Elisabeth Vincentelli