Congrats on picking up a very cool old gun! I don't think that I could bring myself to cut up an old one now, but I would love to find one that have been customized like that in the past.

I went home and looked in my copy of 'A history of the Colt Revolver' by Haven and Belden, and I am pretty sure based on that and some other lesser reference materials that the checkered trigger and backstrap are factory original. That was apparently done to a several models of Colt DA revolvers pre1940.