Blocks can crack from freezing, or a con rod punching a hole through, but iron blocks seldom crack from heat. If the block gets that hot, more commonly the pistons will already be melting around the crown, and leaving scoring marks on the uppper cylinder walls, not to mention the scrape marks on the pistons, and things like stuck piston rings.
The heads get a lot hotter than the block when overheated, so a blown headgasket (due to a warped head or heads) is more likely. With extreme overheating the valve springs can get detempered too - so figure on new v. springs, or testing of the old ones. Also replace any core plugs in the head.
If you take the heads off and the cylinder walls are scored - the next step would be a full rebuild. If they arent scored, and the glaze is still good - you might be lucky.
But Do a Compression Check Before You Tear it Down, to map out how many cylinders have low compression. If its only the one or two that adjoin where the gasket burnt which have low compression, you may not even need to replace the pistons. If other cylinders have low compression - it could be the rings are stuck in the grooves, due to the pistons having begun to melt.