Just my thoughts about the barrel mount portion. But I'd not drill holes in that thin little lower rib and risk gouging the barrels with a drill point or tap. A simple base soldered on the barrels will be reversable later by simply heating and removing it and reblueing. No rib removal and replacement and re-laying ribs, etc. Besides, you'll get more soldered area than the thin line of solder joint for the lower rib. It's not such a big deal soldering on barrels.
Turkey (paper, not birds) shooters will often use epoxy or gorilla glue for gluing on sights and for securing "sleeved" chokes. Easily removed with heat. Definitely not an old world technique, but reversible and requires not much in the way of technique. Epoxy doesn't stand up to freezing temps, however.
