An assembly for an aircraft gas turbine propulsion engine includes an engine nacelle and a thrust reverser. The engine nacelle is configured to have at least a portion of an aircraft gas turbine propulsion engine mounted therein, and includes an intake end, an exhaust end, and an outer surface that extends between the intake end and the exhaust end. At least the engine nacelle outer surface proximate the exhaust end has a semicircular section and a noncircular section. The thrust reverser includes a forward end, an aft end, and an outer surface that extends between the forward and aft ends. The thrust reverser forward end is coupled to the engine nacelle exhaust end. At least the thrust reverser outer surface proximate the forward end has an arc section and a noncircular section. The arc section subtends an angle greater than π radians.