The two Austrian ledger numbers, 1920 and 25, are not related to the 1940-45 German proofmarks. The German I does not stand for "Import", but for "Instandsetzung" = overhaul, repair, a reproof mark indicating rebarreling. As I miss the usual post-1940 proofhouse and date stamps in your photos, it was probably rebarreled (again?) to 7x57 in early 1940 by either Edmund Keller, a Zella-Mehlis barrelmaker, or Wilhelm Keller, Suhl barrelmaker, or Heinrich Keller, Suhl, a repair specialist. "Heller" is not likely, as I know about only one Heller, active in Zella-Mehlis in the 1920s.