Well, it turns out to be a double edged sword - it is indeed a Model 53 22 cylinder, and it fits/times up nicely, just as is; the down side is that the barrel/ cylinder gap is "0", and the face rubs on the barrel. The endshake is only about .002. Normally, when I would fit a cylinder, I stretch and face the yoke, and be done, but it this case, I'm reluctant to do this because the yoke is fit to the Jet cylinder. Do they make .001 shims for the .22LR cylinder I can use? I've only seen .002 and above, and have never liked to use them, but may have to .