The trimming is needed inside the fender, on the side closest the door....this needs to be cut out to give clearance for the new hinge to be able to open up....you can opt to make a custom bracket to replace the one you removed, or just loosen, align, and tighten the fender until you get the desired gap...on mine, i just aligned the fender until i was happy with it...the door/fender gap is perfect as is the hood/fender gap....You can't tell my car has lambos until I open the door up....