The engine is responsible for 250 - 300 lb of the difference.
The iron 5.4 block +100 lb
huge 4V heads, 2 more cams, longer timing chains +70 to +80 lb
S/C & SC drive belts pullys, intercooler +80 to +100 lb
Heavier internals, longer rods, bigger crank, flywheel, bigger vibration damper +30 lb or so.
The 6 speed trannie adds weight.
larger radiator + the extra coolent the bigger heads & radiator hold
Bigger tires, wider wheels, bigger brakes,
the extra pounds add up very fast.