Just emailed flat six innovations on this topic, and they seemed to think that the engine was toast because of the .5 second rattle when it starts up. They quoted me $18,000 for a new one.
Wow. Really?! Gosh, I guess I'll be needing a new engine as well!
My 2.7L is getting a new IMS/Clutch/RMS shortly and my Indie says he here's a slight rattle on startup for a few seconds. He attributes it to the chain tensioners/ramps, or, more likely, worn out plastic camshaft brakes (Pelican Parts -- $19.95 for the set).