I know someone that welds cast iron. I was wanting to weld it up and use it.
Even if the crack is external, you'll need to strip the block down to bare bones to get a good weld. It will need to be pre-heated, peened, and post-heated, then buried in sand to do a very slow cool-down. Do a complete overhaul while the engine is apart, and drive it for another 50-something years!
If you don't want to go to the trouble of welding, there's a process called "stitching" where a series of overlapping threaded plugs are used to patch a crack.
Jerry
