This is the first time I have seen anything like this. How would the barrel insert have been installed? Solder? Press fit? At this stage of the game I guess this is a permanent alteration.
The way these things used to be made was to drill out the barrel, turn a barrel blank to be a snug fit and soft solder it in place.
Usually a bronze bore brush was used with flux and soft solder to tin the inside of the drilled out barrel, then the liner was tapped in place and the two were heated until the solder melted and soldered it together.
The chambers were done the same way.
When re-lining a barrel today, a Loctite type anaerobic locker is used since it requires no heat.
Another technique to insure the liner doesn't creep forward is to machine a slight flange on the rear of the liner and a corresponding recess in the rear of the barrel.
The slight "step" prevents any chance of the liner from moving forward.
"Back in the day" a number of gunsmiths would convert Colt Single Actions or most any double action revolver to .22LR.
The only tough part when converting a DA revolver was modifying the ejector to work with .22LR ammo.