Why did I spin a main bearing?

Just wanted to confirm, you said that "chunk" came out of the oil filter? I don't believe it could get thru the pick up.

I don't believe the cam would move that much with the cover and f/p eccentric in place, dont think that was a problem.

One cam brg. in perticular looks scarred but that could have come from removing the cam and catching it with a journal or two.

Still looking and thinking.