SW On the inner left wing of a B747 is attachment points for an engine to be mounted for carriage purposes. The fan section of the engine is removed and a collar is fitted to prevent airflow through the core section - thus no rotation whilst in flight. Most modern high bypass engines are modular in design so that they can be separated into sections and transported in the hold of aircraft, however, a lot of man hours are involved in the dis-assembly and re-assembly of the engine prior to fitment, so, often the 5th podding of an engine results in an aircraft being returned to service earlier. Whilst flying with a 5th pod there is a disturbance in the airflow resulting in a noticeable buzz in the cabin (& higher fuel flow).
Centreline thrust is great but multi-engine is better. The only aircraft that I can think of that had centreline thrust with more than one engine was the British Lightning interceptor. Great aircraft in a straight line but lacking in turning ability and range.