Weld it or sew it, doesn't really matter, but get somebody to do it who knows what he's doing. Weld repairs need to be done by the preheat-weld-post heat-peen method, where the block is brought to a moderately high temperature with a torch, then a short section of the crack is welded with nickel-alloy rod, them heated again, and stress-relieved by peening with the pointy end of a welder's slag hammer as it cools. I like to keep my welds to 1/2"-3/4", and peen the weld for about 5 minutes before doing the next section of the weld. Once the entire crack is welded and peened, heat again, then bury the block in sand and let it cool overnight. The preheating, peening, and slow cooling prevents stresses from forming that will cause the block to crack right next to the weld from cooling too fast. "Sewing by installing overlapping threaded plugs is a lot simpler if the crack is in a place where it can be drilled and threaded.
Jerry
