Finegunmaker,
I think your making too much out of the opening up of a Mauser or particularly a M-70 (it is 375 Length to start with)and its been done like that for several decades without even a hint of a problem, only a few that theroize on such...

That aside the 9.3x64 is one of the most overlooked rounds in the modern world...It is simply the best all around cartridge ever designed...

It will send a 320 gr. Woodleigh down the hall at 2500 FPS, or a 285 gr. bullet at 2700 or a 250 gr. at darn near 3000 all with good handloads and a 26" barrel..hard to beat that...Its only draw back has been brass availability but now Huntingtons is handleing Horneber and its the best...also 9.3x64 brass can be had by turning off the belt of a 338....

A lot can also be said about the 9.3x62.. With a long tube its a wonder gun...