From what I understand the balancer wasn't tight enough or came loose...the crank is a older Crower casting with a single keyway that extends into the timing gear slot only 3/16 of a inch and if the balancer comes loose at all this is what happens.
Newer castings have three keyways which seems to be much better design.
the carnage is pretty bad ...bent every valve ,some pushrods, maybe wiped camshaft ,still assessing the damage