Re: Colt 22 Conversion Unit
If it is for a collection the ACE is OK but if you plan to shoot it you are much better off with a modern 22 conversion unit.
The absolute accuracy king (on a par or even better than a S&W Model 41) is the Marvel Precision Unit One which ties the entire barrel assembly to the frame with only the bolt moving to the rear. It has a bridge type sight mounting scheme so sights do no move as they are tied to the frame as well. They offer two sight rails, one with sights mounted and the other for scope mounting. The accuracy is so high on this conversion that it is rated at 50 yds not 25 yds which is pretty much the industry standard for pistols. The group that comes with the gun (supposedly shot from your conversion unit) are really impressive!
For a tactical 22 conversion there is the Mavel Precision Unit Two, the Ciener, and the Kimber. These all look like and operate more like the standard Colt 1911 where the sights are on the slide that moves to the rear under recoil. In these conversions, which are blow-back operated, only the barrel itself is tied to the frame. The accuracy of these, while very good, can not match the Marvel Unit One.
I believe all to be under $400. The Marvel Precision site is screwed up so I can not verify that. You might want to call them and visit Ciener and Kimbers sites.