The 747-(400)FUW, 400 in parenthesis because that's given, it's the only version produced, would be an aircraft with the Fuselage Under Wings.
By doing this, similar to an AN-124, Boeing would create an airliner with a number of advantages.
1) The entire bottom of the aircraft could be used for cargo,
2) The fuel tank, by being atop the aircraft and through the wings, could extend into the presently un-used overhead space, giving the aircraft longer range,
3) The wings could droop downhill, reducing stress on them as they would not need a strong support to keep them on a sharp uphill diahedral,
4) The hump of the 747 could be streemlined down over the central fuel tank instead of dropping as quickly as it does on current models, thus acheiving two goals:
...a) The aircraft would become more aerodynamic,
...b) A 2-3 row extension of seats on the upper deck.
The aircraft would weigh considerably more than a 747-400, but with larger engines compensated for by the increased fuel tank as described, it would be superior airliner.
This is the AN-124, with it's drooping wings over the fuselage,
Photo © Paul Dopson
What do you think?