Was hoping for more information, or the barrels, but neither has been forthcoming. It's the owner's gun, and he of course may do what he wishes with the remains.
It is frustrating however for those who use our pattern welded barreled vintage doubles to see reports of a burst, receive limited information and images, we all contribute not especially helpful opinions, and then have no definitive answer as to the cause; which could possibly be established as simply as measuring the wall thicknesses. Knowledge IS safety.

And re: the Parker top rib extension. This shows the screw head clearly, and mismatched Parker D4





https://sites.google.com/a/damascusknowledge.com/www/home