A good engine rebuilder can often weld that crack. You might want to have that discussion with them. The overhead valve heads on heavy tractors, trucks, CATs, are ofter cracked and welded. Even though the N has valves in the block, it can be a candidate for welding or stitching. The thick wall sleeve will keep exhaust and antifreeze out of the cylinder. If the rest of that block is good, I think you will be $$ ahead to have it repaired. Any other block you might buy is just another crap shoot.
Paul in MN