Quarter panel

So do the 71 Demons have the tabs on the back of the quarters that go behind the bumper like in this pic?

Yes.

On a different section - the door jamb - It seems many of the quarters are too short to the top corner of the jamb, needing a pie slice section opened and a small section added to get the gap right. The bottom line - make sure the hinges are in good shape and door aligned first, and check you gaps carefully.