It never ceases to amaze me why the 9.3x64 isn't so popular? It is as good as the 375H&H but in a smaller package & predating Ruger's 375 idea by some 80 years!
If this is a genuine MS then it certainly will be a rare bird, but they were made!
Will need to look at Table 1
http://www.mannlicher.org/aboutmannlichers
Hope it works out for you grandveneur
93x64mm