I think tdracer is most probably correct about not having certfied a three engine ferry with the engine missing. On a 747 Classic, the normal three engine ferry procedure was to sprag the damaged engine so it wouldn’t rotate and leave it on the wing.
The main handling issues with a failed outboard engine were directional control on the runway and the critical period during the take-off run when it is neither possible to continue nor to stop if there is another engine failure. In effect, there is a short ‘gap’ of about 10 knots of airspeed between V1 and VMCG, typically around 130 and 140 knots respectively. If an engine fails when the airspeed is below V1 there is room to stop (just) before the end of the runway. If the engine fails after passing this ‘gap’, the aircraft is above VMCG and you can continue the take-off with just enough rudder control to keep the aircraft straight. If the engine fails within that 10 knot ‘gap’ you can neither stop nor continue. If you try to stop, you will go off the end of the runway doing about 50 knots despite using full braking. If you try to continue, there is insufficient rudder control, it is impossible to keep straight, and you will career off the side of the runway doing about 150 knots.
The other problem is directional control during the first part of the take-off run. With full rudder applied to counteract the asymmetric thrust, you hold the aircraft on the brakes while spooling up all three engines. Then, you release the brakes and the flight engineer opens up the two inboard engines as fast as reasonably possible. Once you start moving you open up the outboard engine yourself, keeping the power just within the capability of full rudder control – in effect, steering the aircraft with the engine until you are above the critical control speed.