Originally Posted by dddd

It would be useful at this point to observe and possibly photograph the dropout/axle engagement from below and forward of the dropout. Good photos so far otherwise!

Is your bike one of the Austrian-built bikes? Mine has a very different-looking dropout attachment to the stays (appears to be welded), and btw I was able to use the PC950 model chain (even narrower) on the old Agrati-pattern chainrings.