Yes, the barrels are 20 inches. The chambers are 2 5/8". And, while I was uncertain as to the strict definition of "on face," I did insert a sheet of typing paper between the breech face and the chambers and closed the action. I could hold the weight of the shotgun up with the sheet of paper, and opening the action was harder with the paper in place. I assume this means it's "qualified" (?). There is absolutely no play between the receiver and barrels when the action is closed.
Here are some pictures. I had forgotten to note that the right hammer is a half-finished replacement. A tool-and-die maker friend of mine helped me measure the original (left) and fabricate a new one on his computer-controlled machinery, although he didn't tackle the knurling at the top. Elsewhere recently I have seen some discussion about whether or not the square that the hammer is mounted on is tapered or not; the consensus I had reached with my machinist friend was that there was indeed a very, very slight taper. We machined a graphite EDM (electrical discharge machining) tool to make the hole in the hammer, and then "depthed" the taper such that the hammer "bottomed out" before the shaft it was mounted on cleared the hole. This ensured that the screw would pull the hammer tightly against the lock. Obviously, any looseness in the hammer would only get worse over time.
If I can get some firing pins, it will incentivize me to finish that hammer!
I want to emphasize that I'm posting these pictures not because I think this shotgun is in the same league as the beautiful, engraved Parkers I've seen posted here, but simply to show how these magnificently well-built shotguns were also put to more prosaic uses, in the hands of security personnel in bygone days who counted on their top-quality construction.
Parker on the wrong side of the tracks
Threaded Mode