In the late 60's/early 70's the fuel guys would run iron blocks until the crack got so bad that they had to chisle the main bearings out because the material would flow into the crack as it got bigger. I think the record for the Bob Banning team was 70 runs from an iron block on Nitro.

The moral is they ran cracked blocks many times. For a stock resto, I would look and see if it could be welded, or run as-is.