6.0 ls rocker arms clatter

[AussieinNC]

This sounds a lot like a missing or defective oil gallery dog bone...the factory ones are made of plastic and sometimes fail, resulting in oil bypassing the filtering process and upsetting the oil flow throughout the engine.

The dog bone is located in the main oil gallery, drivers side of the engine, accessible under the rear main seal retainer....

See link for a video explaining its role....

https://www.youtube.com/watch?v=V7p0h2VwGP0