CIP max cartridge oal is 85.6 mm for the 9.3x64. Jon Speed, Mauser OOSR, gives the factory magazine dimensions of commercial Oberndorf sporting rifles. 8x60, 9x57, 10.75x68 = 84mm oal. 9.3x62 = 85mm. .30-06, 7x64, 8x64 = 88mm (opened up to the front), .318, .333J, 9.3x64 = 92mm (opened up front and rear). IMHO a 9.3x64 with the bullet seated to 85.6mm CIP oal will quite well through an 88mm magazine. Even an 84mm box can be filed ot front and rear to take the 9.3x64. Of course, such a magzine will take only three of the fatter cartridges. Post WW2 many standard length ex-military 98 actions and magazines were opened up to take even the .375 H&H. Even the FN/Browning so-called "Magnum" action is merely an opened up standard length one. Mauser themselves used Magnum length actions with a 95mm mag for such numbers.
BTW that 9.4x64 rifle sold for EURO 514.99, about $ 670.-. Here are some auction photos:

IMHO the design is influenced by Art Alphin's A-Square "Hannibal" rifles of years gone by.