FWIW, duv was Berliner-Leubecker Maschinen Fabrik, Leubeck plant.
The G.43 is not especially ammunition sensitive; any issue 7.9 ammo or equivalent "8x57JS" should work fine. If the rifle still has the stamped receiver hole cover (the little tab about 1x3 inches), I suggest removing it before firing; those things often get in wrong and are bent up in firing. Note that almost all WWII era ammo (and a lot of post-war) will be corrosive, meaning the rifle must be well cleaned after firing, with special attention to the gas tube and piston.
Jim