Well the six pack intake is a good intake up to a point but I don't think that point includes 700+ hp. If you build a nice RB based 505 with good heads like the Trick Flow 240 and a pump gas compression ratio of 10.5 or so then you might be able to squeeze out 700 hp if you have a really good intake manifold and a big carb and fairly aggressive camshaft.

But as soon as you pull off a really good single plane intake and replace it with a factory six pack intake you are going to lose a bunch of power. I did a dyno test a while back where I tried a ported dual plane intake on a 800 hp race engine. We promptly lost 100 hp and the EGTs went crazy due to fuel mixture issues.

There might be some FAST guys who have figured out how to squeeze 700+ hp out of an RB engine with a six pack intake but I'm guessing that it took a lot of compression, a bunch of porting and a fairly big cam.