Getting here a bit late, but I've a 16 ga. DHE on a No. 1 frame, #228929, that at some point had a set of 20 ga. Vulcan barrels added/fitted/& numbered to the gun. Both sets are 32" in length. This gun came to me from a PGCA member here some years back, all shipped in a very nice, 2-bbl. LOM case. (You know who you are, and 'Thank You' again.)
The 16 ga. Titanic set came with its original twin ivories, is still choked full & full, and shows an 'unstruck' weight of 3 lbs. 12 oz. The rib is concave, matted, and roll engraved. Width of rib at breech end is .540" tapering to just .255" at the muzzle.
The 20 ga. Vulcan ejector barrels came with a single factory metal bead that I removed and replaced with vintage twin ivories after rust-bluing to match the 16 ga. set. 'Unstruck weight of this 32" set is 3 lbs. 8 oz.; still choked factory full & full. This rib is also concave in cross-section, matted, and roll engraved, though it is not as tapered as that on the 16 ga. set:
Width at breech end is .510" tapering to .320" at muzzle.....
FWIW, weight of the gun is 7 lbs. 8 oz. with the 16 ga. barrels having a MWT of .028". MWT on the twenty ga. set is .024" and likely unmodified. Fun gun to shoot providing I have enough spreader loads on hand.
All Best,
Rob