From the 747-400 AFM:
In the event one main landing gear cannot be extended, land with all
other landing gear extended.
In the event neither body landing gear is extended, the airplane may
tip tail down when on the ground. Under this condition, the escape
slides at main doors 1L and 1R will be unusable.
The GEAR OVRD switch should be used to prevent the siren aural.
After landing with one or both wing gear not extended, turn the
airplane on the ground only at slow speed.