Oh, boy! Now you understand the SVTs. This was one of the reasons they stopped machining the groves in 1941 - every mount had to be basically made to fit particular rifle, just like their mags.
If I were you, I'd left the mount alone, as we have no idea what kind of steel they are made of, but if you are simply desperate to zero the scope, you can probably put a large dowel in place of a scope and try to twist your way to zero, or use a lead hammer or rubber hammer. Don't blame me if the mount breaks, like I said above.