There are probably piles of real "field expedient" snipers out there but impossible to verify with certainty as anyone with a file can try to do it. It was a real plus of the design that any SVT 40 with the side-rails (ie most built in 40-41) could be so simply converted to a sniper- possibly with the bracket from a true original sniper that had been damaged beyond repair. Not many other sniper rifle systems allowed this option to field armourers. However, I'm not so sure the true Tula snipers didn't have some other features like barrel axis well aligned with the flat receiver sides that the bracket slides onto. I have a number of true SVT 40 snipers and the repro brackets are well collimated to the bore in each case. As an experiment I made my own "field expedient" conversion with a standard '41 Tula and found that the post , when zeroed, was almost too far to the outside of the field of view to be usable.
With regard to the infamous notch, there are photos of real ones now posted all over the place so it seems silly not to show them in a thread. In addition to a very distinctive shape (which is not easy to duplicate) I've taken a micrometer to my 4 and found the location of the front/ rear and depth of cut of the notch to be very, very uniform from rifle to rifle (as measured from the rear of the receiver). Obviously Tula machined these notches as per very strict guidelines. The notch shown in this thread for the rifle under discussion doesn't remotely resemble a "real" one. A field conversion? Certainly could be.
Ridolpho