The eBay bar & ring are not a compatible set anyhow - bar is late while ring (highly suspect) is early. Al Frasca has the best parts.

When I said the sight was "later" than the barrel and receiver, I was referring to apparent date of application, based on wear and color - not design/model. However such decisions are better made in the flesh, as the camera/lighting can play tricks. The barrel appears to be a plausible/possible in or immediately-post-service replacement, whereas that sight could have been added in, say 1920.  My suggestion that a later (but heavily worn and brown) sight be applied was based on the later barrel, but, you absolutely are correct that the 1873 stepped sight DID continue past the period of proof application. The fact that it is the rifle version precludes it being done at SA.

I think that someone who was not aware of all of the little nuances was trying to mock-up an early carbine and, for some reason, never finished the project, which presents you with a fun opportunity to pick up the torch. Enjoy!