Skinned and ready for bodywork, the completed door has had all of its internal mechanisms installed, to check for proper fit and operation. Not only must the hardware work to hold the door closed, the angles and geometry must be correct if the windows are going to operate and mate up with the rest of the hood.
You can see the B-Post extension in this picture, mating with the top of the landau bar and matching the folding window channel extension. The spring in front of the rear fender well helps offset the weight of the hood mechanism, since the whole assembly weighs close to 200 pounds when fully trimmed.