I'd suggest sending a PM to Mooseman. There's very little about antique firearms he does not know. He'll at least be able to tell you what direction to move in, whether to lock it up and not shoot it any more or use it as a shooter. As you said, the .44-40 is more common, but I've seen these in .32 caliber and .44 Russian as well. I don't know enough to advise you what to do - but at least you know what you have now.