Having flown a lot onboard PA 727 as a kid I seem to remember they had two versions of the No.2 engine air intakes: One oval and one round shaped. Must be related to the surge issue. Pan Am in Berlin had early -100s and later -200s. Remember flights from Munich (Riem) with stop at Nuremberg to Tempelhof. Got all those tin "Junior Clipper Pilot" wings back then.