318 Idling fine then started clattering....

75 Duster 318, Started up today and ran fine and idled for 15 minutes or so. It finally died. When I started it again, I heard a pretty loud clattering...

Thought it was sloppy push rods, that wasnt the case.

Pulled the valve covers off and it seem like its coming from below?

Any Ideas?

What the heck do I do know?