I ran up on an Armisport 20 ga. barrel at the flea market. It dropped in, without the lock, but the wedge wouldn't line up. I tapped the tenon out of the dovetail and rotated it 180 degrees and it lined up. I had to make a small end mill cut on the snail, to get it to fit over the lock plate. Haven't had the chance to shoot it yet.
An old pitted barrel could be bored out to .620, if you don't find anything.