The work looks in line with what one would expect for a prototype experiment from the era, but I also have a hard time without a chain of custody or any other documentation-- bearing in mind such documentation may be lost to time if it ever did exist.
These sort of things happen. I have reference books full of "official" examples of Swiss (with the benefit of never being occupied and ransacked) prototype rifles that have A) No serial number, B) standard serial numbers, and C) Specific ranges of set aside serial numbers. Some of these examples are mundane and some of them are really bizarre. It really just depends on the situation-- someone got an idea and either planned it out from inception to be a set aside project, or it's an ad-hoc solution to a problem. I have personally witnessed the same type of things at the Army Research Lab in modern times and they have an extensive collection of past prototypes as well. Without documentation they would look like a real talented "bubba" project. As silly as a necessity to feed from stripper clips may seem to us now, it was always a real concern for people in the region. You need only to look at the development of the Swiss ZFK 55 to see how much work people were willing to put into making it work out. I also remember reading original German training material that made a point to say not to remove the scope from the rail in order to reload via clips. So this adaptation makes sense as to me as something they would try out, but that doesn't mean it's not post-war tinkering or outright faking, too.