In the real world ,if you want to screw up a cast iron repair : arc weld it. That way you can chase cracks till the cows come home. Best repair for that is the lock n stitch repair pins . If you have
not ground so deep that there is nothing left to thread ,you might
be able to use iron tite pins.
I do my share of cast iron repair.
showing cracks in 427 side oiler
Ford block, it froze