As srothfuss said, the engine is big and heavy.
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...