From the markings and description, it does sound like you have a military-origin Mauser 98 action, likely later turned into a sporting rifle. The absence of a maker’s name isn’t unusual—many were scrubbed or reworked during sporterizing. Based on the proof marks mentioned (especially Suhl proofs), it likely dates roughly pre–WWI, around 1890s–1910s. As for rebarreling to 7x57, it’s definitely doable since the Mauser 98 action is very strong and commonly used for such conversions. That said, unless your current barrel is shot out, you probably won’t gain much over the 8x57, which is already an excellent all-around cartridge with similar performance. Before doing anything, I’d recommend slugging the bore to confirm whether it’s .318 or .323. If it’s .323 and in good condition, it may be worth just keeping and shooting as-is rather than investing in a rebarrel.
