When you say race block, how much HP is the goal? Myself personally have seen too many bad outcomes from pushing a substandard engine block. Any engine I build over 600HP preferably gets an after market block. Or an OEM block with filler and good maincaps and girdle. If I was going to use it, I would do a block fill with moroso block filler or similar product. The next question is how and why did it crack? Was it from freezing? or did it do this in a race car? I had a 440 block crack like this, with filler in it already, and the cylinder wall were barrel shaped when I took it apart, so in other words the cylinders swelled and pushed out the side of the block. If from freezing, how round are the cylinder bores?