That's probably(possibly) one of those old pre War guns that went back to the Factory for something simple and the Factory was nice enough to change out the Stocks for a brand new set as part of their "Customer Service" policy!
I'LL TAKE IT!! OOPS,It's not for sale!! Seriously nice find!! I have a 5" and Outdoorsman and am very fond of them!Enjoy the pretty lady!!
Best of Luck!
PackN