Germany and Austria never had their own .450 and .500 Nitro Express versions

See the last post by kuduae / Axel E. in the linked thread or more details

http://forums.nitroexpress.com/showflat.php?Cat=0&Number=399399&an=0&page=0#Post399399

Thanks for the pictures. Are there any further proof marks to tell the story of the gun?

I can't comment regarding sight adjustment. But I think that compared to the cost of an insert barrel a new "Kimmenblatt" is a minor effort.