I ran aluminum main caps and still had the block crack. It was filled with concrete about half way up and and cracked between freeze plugs. The block itself never failed. Personally if you have a light rotating assembly that you don’t spin too hard it may live. I just saved my money and bought an aluminum block. I would not build another cast iron block again, to me it’s not worth it. My 2$. i never had my cast iron junk on the dyno, but with cast iron heads in my dart it ran 9.70 all day long. It ran out of steam about 6700 rpm, no more air left.