You have two choices on fixing that, take it to a cast iron welding shop or have it "drilled and stitched pinned "
I had a 1965 street wedge block that had two freeze cracks and a casting flaw in the crankshaft area at the bottom of cylinder #4 that leaked coolant that I had fixed at a cast iron welding shop in SO CA. The owner wanted that block fixed instead of using a 440 block he had due to it was the proper casting number and casting date for a 1965 Plymouth Satellite he had
I've heard that there are some new cast iron welding rod that any good welder can use now to fix cast iron cracks like your deal, but be careful on who you have try that
I've had several freeze cracked 906 heads fix the other way also, all things are fixable, not cheaply though
Good luck on your deal