When I spoke to Rolf Babick, who made Tony's and now Mick's "Fat Lady". A .577 2 1/2" LNE on a Greener Empire shotgun. Because of the size of the action, the choice of cartridge chambering is limited. Unless one wants some huge thick barrels. So the .577 cartridge was chosen. For a double rifle and a cape gun version.

If choosing a smaller cartridge, and lesser barrels than the action was designed for, such a result as the pictured DR might result. The raised or extended rib and dolls head is obviously required to lock up the closed action.

I think it's pretty obvious that these are a later set of barrels. Either an additional pair of rifle barrels maybe to 12-bore shotgun barrels. Or maybe a replacement set of barrels, maybe to replace a original set of barrels.

I said it looked ugly but if it's usable and safe, at reasonable price, it's not so bad that one couldn't own and use it.

What cartridge chambering is it?

I note it's got Damascus barrels. So is it BPE?