Well, this project has gone a bit sideways. The hand has started slipping on one of the ratchet notches, so the corresponding cylinder isn't locking up tightly. It turns out the slot for the hand is exceptionally wide and the retaining screw is not as tight a fit as one would like, so the hand is slipping sideways just enough to disengage from that particular tooth. I've fussed with it but cannot get it to work reliably, so I will be fabricating a new, thicker hand that cannot move so much in the slot. This ought to solve the issue.
In the meantime I can still test the cylinder- it fits and functions perfectly in my .44 Colt conversion, 'The Dandy.' I've checked and the chambers line up very nicely.
Who knows? Maybe the cylinder will have a new home and I'll fit the .44 Colt conversion to this gun once the hand is replaced.