I'm really not all that surprised. This was a motor we threw together in a two week rush before superlap, and the crank got re-used after this happened last november:
the crank was actually bent after that one and we had it straightened, magnafluxed, and put it back in.
Other than the crack the shortblock that just came out is in good shape. We will probably have it sleeved now and get some oversize headstuds. What I think must have happened is the cracked cylinder let water in the chamber, and that bent the rods and broke the crank.