My one 67 BB has a 4" crack above the front right side freezeout plug. So much for freezeout plugs working.
Anyhow, I drilled stopped it, cut a small depth V in it with a Dremel and filled it in with JB Weld and it has held since 1987.
But, if it starts to leak again, I read of a process to fix cast iron motor parts called 'stitching' (Lock-N-Stitch) and it looks to be a possible solution for cracks outside a block (and maybe for inside as well). It involves a lot of a repeating processes to drill, insert a special screw slug, and repeating the process while overlapping the previous screw slug until the whole crack is 'stitched' and it can be ground down to make a surface.
I just thought you may be interested to know.