My bet is on a broken piece of guide rail or tensioner I would pull the valve cover, turn the motor by hand with the plugs out, and look for normal valve movement sound and action.
If the motor is already screwed, you wont make it worse by hand.. If it turns ok, remove the front covers to expose the entire chain & tensioners. If the chain has not slipped, motor might be ok. Replace the chain, rails & tensioner, drain the oil, with full oil pan removal.
Cross the fingers and try it for maybe 5 miles and drain oil again with plug this time. Stay on short intervals 500 miles or so, for a couple times to clean out oil system.
Where did the valve cover bits go...... try to find.
My .02
Ken