Topgun;
My Lefever guns whether Damascus or Twist have steel ribs. I cannot make any positive statement on this but highly suspect these barrels were imported as Tubes Only, with the ribs supplied by the maker. These makers would not have had the damascus/twist iron available to use.
When the barrel maker themselves actually assembled the pair then he was more likely to make the ribs of matching type metal. Just a thought.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra