The stocker is already very light.  Don't do any trimming..I would recommend adding a 1/4" plate top and bottom set into the "valley " so to speak for the full length of the arm, that brings it up even with the side rails..hardly even noticeable.   It will still be lighter than the aftermarket Chromoly arms and the front section is very strong.  Remember to make the cuts at the 45 degree angle for strength and more weld area.