I installed the Cominolli Full Length Frame Saver Rod on my Colt Officer's Acp; It too required the fitting of the reversed recoil plug. Ed Brown once did an article on how much to remove from the slide for the tapered shoulder on the plug. I simply filed back the same thickness of the plug's shoulder to accommodate the fit on the slide. Another important thing is to make sure the recoil spring compresses fully into the plug when the slide is recoiled.One way to check this out is to place the recoil plug on the muzzle end of the slide, with the bushing and barrel removed, and push the rod and spring through the plug by pressing the rod head against a table top.
You will also notice this rod has an Inner and an Outer shok buff; This provide buffers to the slide and the frame, totally eliminating the metal to metal battering from this shorter recoiling pistol.