I have been comparing the lines of the stock and the checkering pattern with photos of Neidner rifles in Michael Petrov's books and in the upcoming Amoskeag auction of Michael Petrov's collection. The Neidner-Sukalle I just bought has the typical lines and checkering pattern characteristic of Neidner's work. I'm persuaded that it was done by Neidner.

The sling swivels are missing. They seem to have been the same swivels found on this rifle in the Amoskeag auction: Custom A O Niedner Model 1924 Proprietary Action B - by Amoskeag Auction Co - http://is.gd/Xbd08p

Can anyone recognize the make & model of the swivels?

The picture is much clearer in the actual catalog.