Filling a block does not strengthen the weak areas. ALL it does is help with bore distortion when you get the bores bigger than they really need to be, given the thickness of surrounding metal.

Now, not being a small block expert, I really don't know what is considered the weak area of a stock block. Is it weak in the mains, are the bores thin, is it the caps? Someone who knows more than me would have to answer that. Whatever is perceived as the weak area needs to be where your focus is. Pouring it just to pour it won't help if cylinders are not thin