The production list approved stock 3 model doesn't have slide ports, so the OFM replacement slide would not be the same contour as the original slide, even if the Stock 3 has a cone barrel (which I don't think it does). Once the Stock Master is on the list, I think swapping a limited complete slide/upper on a stock 3 could go either way (the color is covered by 21.2a). It depends on what the "original model of gun" is. This isn't a P320, an STI frame, or a Zev receiver. The stock 3 frame says "Witness", not "Defiant".