The (square) AC says made in 1977.
The proof marks say it has been fired at least once.
The nipples are missing.
The failure to index and lock sound like the hand spring and the trigger/bolt spring are broken, bent out of line, or missing.
An Armisport reproduction was made by Armi Sport in italy, the company now doing business as Chiappa... with no current revolvers.
A search found a gunboard post in which an Armi Sport was said to accept a Uberti cylinder. I would want a return guarantee from R&D or Kirst before I paid for a conversion cylinder, those things are more expensive than the value of the revolver.