[Hugh]

("A question for the gunsmiths in the audience, are the receiver threads on a Luger cut such that, if a mm was shaved from the front of a long receiver, would a short-frame barrrel's feed ramp, front sight, and extractor notch line up properly if it was screwed into place?")

Dwight,

Yes, although it might take a little more or a less depending on the particular reciever and new bbl. A "long receiver" is actually 2mm longer than a "short receiver". However the receiver on this gun seems to be a little bit shorter than the frame, and the way that the front part of the first proof mark is almost gone is a good indication that your premise is correct!