I saw one a month or so ago at JBARACING in San Diego. It had a Whipple blower and put 650+ to the wheels with just the new blower and a 3" JBA exhaust similar to the one on my Cobra.
513 RWHP with JBA longtubes, X-pipe, exhaust, tune...custom CAI in the works. will re-tune after that...should be in the realm of 530-540...will keep ya posted
check out dynospeedracing.com and scroll down on the home page, they got 704rwhp out of a GT500 with Kenne Belle and custom tune, NO other modifications...I have seen the car in person