I am the guy who made a model 19 cylinder into a model 53 cylinder.
I took a recessed model 19 cylinder and fit it with a K22 extractor, then I drilled and reamed some 4140 roundstock at .222, you could use an old 22 barrel, then I turned 6 pieces to just fit in the model 19 cylinder. I did steps in the inserts for the throats, but reaming the chambers straight though would have worked. Then I fixed the inserts in the chambers with red loctite after cleaning them well. Once that was done I turned the excess of the inserts sticking out the front of the cylinder flush with original face, and did the same with the back side, plus machined them flush to where the ejector sits and then ran a 22 lr reamer in each.
It really wasn't that hard, just time consuming. But, with model 53 cylinders selling north or $600, worth it to me. I think I got the parts for a bit over $100 and shop time cost me nothing. IF you had to pay someone to do it, it would probably be cheaper to buy a complete model 53 with the 22lr cylinder..
You could also do it by using a K22 cylinder, remove extactor, drill and ream each chamber to 3/8", make 3/8" inserts that stuck out the face over 1/8", reamer the inserts to 22lr and trim the inserts to get the right gap to a 53 barrel shank. You would also need to make an over length gas ring. The inserts would of course, stick out the cylinder face and look "interesting"
19 cylinder conversion to 22lr mdl 53
It shoots as well as any of my other K22s