Regular epoxy won't- - - -Marine-Tex is designed to be flexible and waterproof. The block surface MUST be clean and it helps for it to be as dry as possible. Drill a small hole (1/8") at both ends of the crack to keep it from spreading. The crack should be V-grooved for the best results. Just as the patch material is curing, press a piece of 40 grit sandpaper over the surface to duplicate the texture of the surrounding cast iron. That's just cosmetic- - - -it hides the patch after painting.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!