With the stock forged crank and rods you're safe at mid 500-600HP that being said you're pushing it with stock rods at 600 in my opinion. The block itself is good for 800HP.
Terry, you've been a lot of help in this thread, thanks! I'm a little confused by the above statement though. The stock crank and rods in my '72 440 shold be cast iron, right? Was the rotating assembly forged from the factory?:dontknow: