I wouldn't buy a block with a crack in it. Having said that, I have been running a 216 with a long crack in the water jacket for 25 years. I had it welded which slowed it down. I added some stop-leak and reduced it to a tiny weep. Since the radiator cap is only 4 pounds, there doesn't seem to a lot of pressure on the crack. Maybe over time, the naturally occurring sludge will seal it up even more. I am just not ready to give up on the ole gal yet.
