Just a thought, but I believe I'd drill a hole...maybe 1/8" at each end of that crack and then bevel grind it all the way across. Then I'd take a 1/16" brazing rod, measure and bend each end so they'd fit into the two holes and lay the rod in the crack. Then I'd use a flat point hardened chisel to tamp the rod into the crack as tightly as possible. Then I'd use Stay-Silv paste flux, an oxy-acetylene torch and some Stay-Brite silver bearing solder and just solder it all the way across. It wouldn't get the block hot enough to do any damage (that solder melts at a temp just below 450F) and ought to be plenty strong enough to last a long time. That solder is fine for joining dissimilar metals and you can definitely use it on cast iron. In many cases Stay-Brite is stronger than a brazed joint.
Otherwise, I'd say stitching it would be the best answer.
