There's some other things that can make a difference on what you are wanting to do. The depth of the recoil shield surface in the frame is an important one. I've never checked this depth in a P-13 compared to a P-14 as I've never had a customer request what you are wanting. However in a government model the depth is .775 where as the commander is .710. The surface area that I'm refering to in the frame is the area that the recoil guides shield (or head) is against, so when the slide recoils and the spring tunnel of the slide contacts the recoil shield the slide will be traveling farther to the rear before it stops rearward movement.
Also in a commander length gun the skirt on the barrel bushing is shorter and the contact area on the front of the chamber is set back farther. These are all things you may want to consider before attemping your project.