About the best I can figure, and it is only my guess, the knurled ring adjustment probably was dropped about 1904. A spring and plunger inside the finger lever was used for a very short time but I think that was after the ring was dropped.
Most have no adjustment there after and suffer from lever droop with a bit of wear or a diet of HS ammo.
The later Model 1915 Favorites are no stronger,,in fact actually bit weaker IMHO as the breech block is made so it does not contact the rear wall area at all when closed.
There was previously a tension screw on the step of the breech block accessable when breech is open. That was used first, when the extractor was at the 7 o'clock position (also on the Sideplate Favorites and the Model 44).
When they moved the extractor to the 6 oclock position, there was no room for it anymore.
It remained an extractor in the 25&32 rifles and smooth bores, while it became a spring loaded ejector on the 22RF rifles.
I understand they made the smoothbores in 32rf as well as 22rf, but as I said, I've never seen either that I can recall.
The tang sites are a hole spacing specific to Stevens,,the screw dia/thread is also,,being quite a bit smaller in diameter than most other mfg's.
If you really want a tang site on a smooth bore,,
there are some repro's of the Stevens sights around.
The one supplied with the Favorite was a simple affair, though Lyman, Marbles ect made their usual hardware for the Favorite as well.
Here's a link to one from Jeffs Outfitters. It's actually for a Model 44 or one of it's varients. A little much for the Favorite and I think the hole spacing is wrong for a Favorite anyway.
But it gives you an idea what may be out there.
Jeffs Outfitters - Rear Sights