Small block bottom build horsepower limit

PROSTOCKTOM said
You might be safe to 600 HP if you have the engine tuned properly, run proper fuel, and have a quality damper on the end of the crank.

Once you get above that level all bets are off on an OEM block.

Tom

Rick Ehrenberg has stated about the same thing, 550-600 IF you fill the bottom half with some type of concrete to stiffen the block.