Max HP for a 99 cobra?

i have a friend that just picked up a 99 cobra and would want to hit around 500+HP is it possible with stock bottom and heads? will he be able to get that with some kind of a power adder like a kenne bell and an exhaust? what is needed to get to that range safely?
i have a GT and i now that it pretty much max's out at 400HP safely, but that engine has a forged crank (right?) and those wonderful 4V heads (I’m jealous) what is needed to get to that.. its a 5 speed and he wont be hitting the track but 1-2 a year if any.
thanks any info would help out.

so the only the forged crank and those 4V heads are the main differance between his 99 cobra and my 2000 gt? so does that mean that if we get the identical chargers, exhaust, and a few mods here and there. that we can still be the same ET and same HP?