Where is the crack? If the 46 is running the original cooling system, it will have a "zero pressure" radiator. That means a crack repair shouldn't have to seal any pressure. I'd suggest an aggressive cleanup of the block surface such s sandblasting or bead blasting, drilling a small hole at both ends of the crack, grinding a shallow "V" and using Marine-Tex to cover it. To give the patch the proper "cast iron" surface texture, press a piece of 40 grit sandpaper over the patch as it cures.
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
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