I remember a 10,75x68 that was for sale in Denmark years ago now but is still on the website and look on this rifle again.

http://www.huntershouse.dk/kat408-Rifler/side645-G.G.-Co.-%E2%80%9CKaba%E2%80%9D.html
barrel is marked "G.G. & CO, KABA “og “ KRUPP LAUFSTAHL, 10,75 x 68" to bad no serial number but I am convinced this is another modified 10,75x57.

clearly the second modell