I'm not sure that would work. I think the ejectors are different between the .45 and 10mm and the .45 ejector wouldn't work reliably, possibly at all, on the 10mm. I believe that's the reason that you can do so many conversions on the 20, that you can't do on the 21. If it were just a matter of filling out the hole in the slide, then anything you could do to a 20, you could do to a 21.