Hello Brent,
I agree with the use of the word 'alleged' in this instance. The rifle does appear to have many attributes that would seem to be of Zischang' origin. But, there are some modifications that would appear to have be added after A.O.Zischang died in 1925.
Looking at the photograph of the left hand side of the action, there are three modifications that look 'post' Zischang.
1. The presence of a gas relief vent on the upper side of the
breechblock. An addition applied to some rifles altered to
take high pressure cartridges, where primer piercing may
take place. (1930's onward vintage)
2. The addition of two screws above the large diameter 'Plug'
screw on the left side of the action body. Neither screw has
any useful purpose other than perhaps to be the anchoring
points for a side mounted rear sight. Hardly a likely
addition made by Zischang as he attached his typical 'Dolls
Head' mounted upper tang site base, which he fitted to the
Military Borchardts he modified.
3. The small cap screw near the rear upper rear of the
breechblock which permitted access to an adjusting screw set
in the firing pin which enabled the depth of sear engagement
to be adjusted. This latter item was first described and
published in The American Rifleman for Sept. 1946, years after
A.O.Zischang passed on.
An Zischang modified Borchardt? Certainly in many parts, but in my opinion altered further at a later date by person or persons unknown.
Harry