A crack in the block, especially in the water jacket can be succesfully repaired and virtually invisable. Keep it and fix it would be my advice.
Cast iron cracks are usaully repaired by starting a little past the start of the crack. First a hole is drilled and tapped. A tapered set screw is inserted and tightened to the pointn of twisting off. The screw is ground down flush with the block. Next, moving along the crack, another hole is drilled and tapped. But, the hole is overlapped slightly onto the previous hole. Again ground down flush with block. This process is repeated until just past the end of the crack.
