I once saw a 747 (I'm pretty sure it was TWA) do a 3 engine ferry out of Cairo. I believe it was flown out by a Boeing crew, who were sent in for the job. It did seem surprising, as the 747 was capable (I know, because I've experienced one) capable of carrying a "fifth pod" engine under the right wing. If a replacement engine was required, one would think it was better to bring an engine to the U/S plane rather than ferry it on 3 to the engine.
Where was the 747 ferry going? I'd be surprised if they had planned to send a 3-engined 747 across the Pond - only BA does that.
TWA may have judged that getting the aircraft to somewhere that they held a spare engine (Paris/Frankfurt/London?) would get the aircraft back in service quicker than tying up another 747 to transport the replacement engine.