Try applying a layer of Marine-Tex over the crack after sandblasting the area or roughing it up a little with a flap wheel on an angle grinder. As it's curing, press a piece of 40 grit sandpaper over the patch to simulate the surface roughness of the surrounding cast iron. Lots less expensive and quicker than metal stitching.
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!