I was thinking you should ask Colt. I have a Springfield Champion Milspec with the 4 inch barrel. Marvel said that their unit 1 would work with it. I still haven't got it yet though. They are a bit backlogged.
So I don't know if it will work until I try it myself.
Based on what I remember, it's a liability issue. Apparently the hammer can ignite a .22 rimfire from the half-cock position, defeating the safety which was designed for the .45. Others may correct me on this.
Regardless, I've got a Wilson/Marvel .22 conversion on order at my local gun shop.
I did not know about the liability issue so I put a Ciener conversion kit on mine and run it through it's paces every once in a while..works like a charm and fun to shoot..also have a Colt conversion kit but don't like the way the floating chamber leads up so it is just for looks at this point..hope that helps..all5x