Hoo boy, I don't know. The right side (of the picture) I think will be under the gasket and pump body and probably won't cause any problems.
The left side is another deal. Pretty sure it's open beyond the gasket/pump body. I think I'd try taking it to someone who could repair cast iron and see if a filler piece could be welded in (cast iron rod and/or nickle rod at low heat and then machined flush. It wouldn't be subjected to heat stress like a cylinder wall so it should hold that way. Check into cast iron welding before trying to mess with it.
Before you even do that, however, look carefully at the w/p flat. Is that a crack from the 3 o'clock bolt position I see? If you're cracked into the water jacket you're going to want to clean and Magnaflux test the block before you spend too much money on it.