I'm thinking about building some 496 stroker motors, will a Scat 9000 steel cast crank hold up to 575-600 hp?

It will hold up for a very short periOf of time in a marine app. You really should go forged if looking for that kind of power.

X2. You need forged for a marine engine with that kind of power. The 8.1 liter engine has a cast crank and if I remember right I believe raylar said anything over 500 hp and a forged crank is a must. Same would apply to your engine.

Spend the extra money, and go for the forged crank. You'll be happy you did. Even a basic forged scat or eagle crank is fine.

assuming you are going 454 +060 and 4.25 stroke...below 5500 rpm the cranks will be fine...

It's one of those things you have to weigh out. If your throwing together an engine on a limited budget and a risk taker go for it however assuming your putting some money into this and want it to last go forged. There are some pretty good deals out there. Regardless of what you do a good balance job is very important.

Think of it like your walking across a 2x6 spanded across two high rise bldg tops. You might make it and might not. Then having to do it over and over. lol... I've always been fine with cast cranks however never used one in anything over 500 hp.