Stock -70 340 block with nitrous??

I do not believe that limit of 600hp. BUT! As mentioned, the tune has a lot to do with it between the power and the NO2. Also, how often it is raced. How heavy the load is. (Car weight and effort to move it. The applied effort.)

Lesser engines have died meaningless deaths at the hands of brutal unneeded beatings in heavy cars and over revving.

Where does a stock block break?
Excellent question.