Best way to flush engine after rocker arm failure?

That is my biggest thoughts too, what happened, I have never had any thing back out like these did. I have been building doing this since I was 13, I am now 72.
So this is why I asked the forum as to what they thought. I guess just throw money at it and it will go away.

If I had to "GUESS" I would say that somehow the shaft didn't tighten down all the way. How does the other side look?