The most obvious convertible structural part is the floor reinforcement pan underneath. There are a few other sheet metal differences. You can compare those looking at the two diagrams at http://www.thefirstgensite.com/library/partscounter/illustrated/exter/metal.html Converts from the factory all had vibration dampeners (aka cocktail shakers) in each corner. Although not advertised as a structural reinforcement feature, they were added to reduce body vibrations. Over time, some owners have removed them to reduce weight.