So the first thing I did on mine was to cut them off of the engine cover and trim them to fit. (I have one of RobsLP640 kits where the bat wings and engine cover are all one piece). This was done after my engine cover was cut down and fit first. I think the most important part of the back end is getting the engine cover correct. After that, the bat wings will fall into place as well as the rear trunk. My biggest issue though was that the curvature didnt match up with the body, so I had to make a framework out of 1/2" square tubing. Once I bent and welded the tubes, I screwed them to the panel which pulled it down into place to match the body