Early M21s had a different "brace" It used a screw that came in from the rear of the forend iron "forend shoe" Winchester call it. Look at the rear of the forend from the knuckle radius, there should be a screw head visable near the bottom. If there is, that locks down the "brace" under the iron. Amd if has been working for 70 years I think it will hold up for a lot more, particularly on a twenty.

Dennis Potter