Boney
Add more wing span (at a later date), then throw on some winglets, (at a later date).Maybe there has not been huge advancements in aerodynamics since 69, but I would be very surprised if the A380 wing, designed from scatch, could not beat the 400 (plus any future wing span increases) for aerodynamic efficency.
For those not up with the history and development of the B744 program, the wing on it was a completely new design from the ground up. It incorporated a new aerofoil cross-section, increased span with winglets, a large proportion of composite construction and a completely new wing to fuselage fairing. One could argue this is exactly what Airbus did when they developed the A330/340 series from the A300.