Or, as Edwin_M also suggested, you don't need a shunt loco at all, just provide a runround facility clear of the container handling area, the train loco runs round and then shunts the container train into the handling area. If necessary that traditional railway feature, a set of reach wagons (otherwise stabled in an electrified siding nearby) can be used to make sure the train can be placed in position for loading or unloading without the overhead coming too close to cranes etc, and extracted again when ready to leave.