The B707 is a conventionally controlled aeroplane (cables, bellcranks, balance panels etc), with hydraulic assist only with the rudder, and of course, spoilers.
LE devices are extended pneumatically.
Trailing edge flaps can be extended electrically, if required.
However, if the aeroplane is very heavy, and a sudden power loss is experienced with two engines on one side (3&4 for example), with takeoff flaps at 14 (used on the B-advanced cowl model), sufficient height needs to be traded for airspeed, until the flaps can be retracted, for it to attain a positive rate of climb.
IE, too low, too slow, can and generally will result in being dead as a doornail.
Clean it up however, and it performs surprisingly well....considering.
PS: a 140 pound push on the rudder is required (rudder boost ON) to keep it straight, at lower speeds, with failed engines on one side.
Boost OFF (or failed), bypass the hospital, and go straight to the cemetary.
To give you an example of the necessity of rudder boost on the B707, with one outboard engine failed, Vmca is 120knots with rudder boost ON, 180knots with boost OFF.
Two engines inop on one side, Vmca 170knots with rudder boost ON, 235knots boost OFF.
A tough old bird, but it needs to be handled with care.