http://www.ussrphoto.com/UserContent/1932016_$_57 (2).JPG On eBay there was this old type (1950) of Jupiter-8 similar to a zk zorkyof the same year. ididn't find in Soviet CAMS.com that lens. Did you know that?
Yes, I have just the same: s/n 5005810. The lens barrel is guided by two screws, when seen at the back. And it has the Sonnar/ZK "ears". Of course, no Zeiss serial number. An intermediate version...