If that was rated at the flywheel an LS3 has it beat by a long shot. In a gross rating the LS3 is high 400's almost 500. an LS7 has got to be in the 600hp range.
The 2014 would beat it on pit stops alone the diference in fuel mileage has got to be ridiculous.
I've had 400+ HP carburated SBC's before they can't compete with the LS3 in my 2013. Hell the delivery is insane too. The chassis on my 1LE surpasses anything I've ever built includong a C3 Vette. To get the kind of power out of an SBC that an LS7 or even an LS3 you would have one of the rowdiest beasts you ever saw.