Thanks to everyone for your observations and comments!
For those interested, Graeme Wright's "Shooting the British Double Rifle" (Ch. 6) discusses the 'chamber ringing' phenomenon as well.
Here are a couple of photos of the rifle showing the folding tang peep sight. I've yet to see another on a Henry double rifle. It is adjustable for elevation only. https://s1243.photobucket.com/user/rmbatten/slideshow/
Also, this rifle has an interesting extractor mechanism. There are two angled prongs or cams threaded to the end of the extractor rod. These prongs fit into slots cut into the water table. When you open/close the action, these angled prongs cause the extractor rod to slide back and forth. Very simple and sturdy, but you have to carefully align them with the slots when assembling the rifle. You can see the left one in the photos as a thin, near vertical white line just behind and above the hinge pin.