I just sealed up about an 18 inch crack in my 54 3100 that had set out in a field in Alabama. I had about a 1/4 inch separation in the middle. Used the metal JB weld that comes in a tube. You mix it my kneading it in your hand. Not a pure fix but a lot cheaper than a new engine.
Good luck on yours.

1954 Chevy 3100
One problem solved doesn’t seem to shorten the list
Montgomery, AL
In Project Journals