First pic is sort of small. Did it split the block right through the sleeve?
Nevermind, I figured out how to make it larger.
How is the crank bushing? Signs of heat/distress?
A quick assumption would be a clearance issue developed at that point, and the crank hammered on the block until it split.?
You broke it good, thats for certain.
Not the same thing, but I have seen 302 Ford stock blocks in high HP situations split the blocks in half. Right through the cam bores and main bores. Pull the intake, oil pan and main caps, and 2 inline 4's fall to the ground.