Happy Thanksgiving!
I finally got some shop time on this. I used the existing front bead to align my bayonet adapter, and file in the rear most notch to lock in the alignment.
I then marked and bought cut back the barrel...mostly square, and hand filed until it was pretty dead on.
Now we have a problem. The bore is not concentric with the outside of the barrel. The top of the barrel has an extra whopping 18 thousandths of thickness! very noticeable with the naked eye. Is this normal for these? I'm not so sure I want to continue. The notch for the front screw is about 18 thousandths deep, and it's location is where the barrel wall is thinnest. the thickness where the last screw goes is 51 thous.