RTF, he's talking about "adding a Simmons rib", not taking off an original and replacing it. So he's talking about a plain barrel Mod 12 vs one with a Simmons, not original VR versus Simmons rib. And I expect most everyone here would agree that adding any kind of a rib to a really pristine Model 12 isn't a good idea in terms of what it would do to the value. But on one that's your basic "shooter" with some wear . . .