Good heavens, how thick are those barrels? Even if you don't get a pound off, you'd be surprised how light a more butt-balanced gun can feel in hand. So long as you can maintain .04" wall thickness at the thinnest point (just prior to the choke) and .2" at the breech, you should be good for reasonable shot loads (no 200gr charges with 3oz of shot
or the crazy loads some on the forum are using to get around the fact that they have cyl. bored guns lol when hunting at modern shotgun distances). That would mean each of your barrels would taper from 1.18" down to .855" at the muzzle. Personally, I would go with a 1.2" down to .89" barrel, to add a little more durability.
You would basically have to remake the gun, in order to not have it look weird (stock fit, lock fit, excessive material between the barrels, re-soldering barrels, ect). Sell the Pedersoli, get a custom piece that fits what you want, in my opinion. They shouldn't cost any more than a Pedersoli for a basic one (or you can go crazy with the gold inlays, engravings, and carvings
).