Ditto on the Hyper's. They're durable, but brittle, and don't take much in the way of detonation. The stock 400 crank should be fine with some decent prep, and good machine work on the block. Like CFM said, 500hp these days isn't radical, but will require some attention to detail, and a certain amount of investment to make sure you don't end up with a pile of scrap after a few hours. The other thing to keep in mind is where you want the 500 hp. It's all together different to build a 500hp circle track engine than a reliable marine engine with the power in a usable rpm range. Do your homework and get the right parts combination the first time and not have to spend wasted time and $$ re-doing things a second time around.
Edited to add: The steam holes in the heads talked about above are a must with the 400 block.