Best way to flush engine after rocker arm failure?

Jomar makes and sells a 100% no bypass oil filter to keep any debris carried by non-filtered oil from being pumped through the motor. It's all I use on my 2 Mopars. Their filter saved my bottom end when I had valve train carnage a few years back.

If you inspect the oil return areas directly under the damaged parts, you will be able to determine how much metal was dropped by the parts as they failed.

You can remove the intake and check the valley as well. If you see stuff down there, pull the pan and clean it too.