I have a novice question concerning sidelocks. Are these gauge or model specific, or are they generally interchangeable from one gun to the next? I have a field-grade featherweight, 12 gauge that I believe from the serial number to have been made in 1929. I have access to some engraved plates but have no idea what gauge or model these came from. I'm wondering if these would likely fit my gun. Are these interchangeable?