Will probably take a little philing but it shouldn't be too hard to fit. I believe the top of the frame is regualr sized but then gets wider down towards the magazine well. It was his idea, but if he is wrong, then we could always just build a custom P14.

Your dad may be right, but if not, I would think it would depend on the thickness of the metal in the slide. If the edges of the slide need to be milled out significantly to make it fit on the P14's frame rails, that might weaken its strength. But if it's, say, a few millimeters off, no big deal.