if you are going to build a motor that makes 500 rwhp then start saving for a dart block right now, my advice is do it once rather than putting $4000 into a stock block only to have to replace it.
If i could go back i would have went with a 351 sportsman block... alot of people dont realize that if you are already buying a dart block then it costs no more money to go with a 408/427. And with a dart block you can have a 466ci small block. A strong 408 with the right parts will make 500 rwhp all day and put a turbo on it and you have a 800 hp street car.
People will tell you "Build a 331/347 so you can reuse your balancer/flywheel etc etc..." but if you are building a serious street motor wit say a 0 balance crank then you cant use that stuff anyways
Save your cash, build it once, build it right, and most importantly BE PATIENT. Take it from me, i did alot of things the wrong way 2 summers ago in an effort to just get my car running and i had to pull the motor out of the car and do things the right way, which wasnt fun or cheap