Thanks for all the helpful posts!
Well, good news and bad news. The rivet was from the passenger side valve cover. The baffle had been "manipulated" for clearance as noted in a previous post. The bad news is that I am missing a second rivet... According to my records, the last time the valve covers were off was 10 years ago. So the other rivet could have been "lost" a long time ago. So now how do I go about chasing it down? The oil has been changed every 1000-3000 miles (once a year) for the past 10 years, so it may have slipped through in the past. I screened the oil this time looking for it, but have not in the past. I did check all around and it is not sitting anywhere I can see. There was no baffle on the drivers side cover, and now there is no baffle on the passenger side...
And Bob, great use of the word "wallerd"...lol
Jim