I looked at a 642-1 about a month ago at LGS. It also said Airweight on side. In fact I woudnt of known it was a Pro if retail tag on it didnt say so, and said moon clips. I pulled trigger on it was not smooth like 2 PC versions I own. So my take was kind of like you said, moon clip machined cylinder on regular 642 and thats about it. No trigger job done I guess. I'm curious what your take is on trigger pull of yours. Is it just stock?