Working on a MJ for a land speed record,  I know jeep offered mirrors that mounted to the sides of the door, so they should have had little block off plates over the triangle holes where the standard mirrors went.    Or if you just had a drivers side mirror, passanger side should have the plate.

The rules say I have to have stock exterior body panels and parts.  I really need some.  Maybe nextime you are in the boneyard, keep your eyes open.