"It also looks like the nipple where a cap would go has a screw in it."
Nate, I looked long and hard at that, too, but that is an optical illusion. Take a look at the other pictures in the thread and you'll see what I mean.
You're actually looking at the hammer cut out and firing pin channel in the back of the breechblock, but because of the angle of the photograph and the shape of the metal cutouts in the breech it looks like a nipple with a screw in it.
As far as I know, no Werndls were ever hammerless/striker fired. The rotating nature of the breechblock would make that difficult (but not impossible) to achieve.
The Werndl was made in several distinct variations over a span of about 10-15 years.
This particular rifle looks to me to be a Model 1873. These apparently were purpose built breechloaders, not conversions. Also, the action was modified somewhat after issues were found with earlier versions.
Ok...
What looks like a "cocking piece" on the rear of the action is, I would suspect, the axel for the breechblock. The smaller screw to the left, along with the plate that connects the two, is like part of a retaining/strengthening assembly to keep the axel.