I found a parts diagram. It is indeed the action that preceded the Python/Police Positive type action.
DO NOT WORK ON IT YOURSELF The hand works the same as does the Python, but the rebound lever (31) is different.
Link to Steves' Pages
I'm wondering if the hand spring (28) is broken. This would cause the hand (27) not to engage the ratchet. Of course, if the bolt (29) isn't dropping, then the cylinder won't rotate anyway.
Finally, don't be surprised if the cost to repair outweigh cost of the gun itself.