The trim all needs to be removed unfortunately. The windshield, back glass and drip rail mouldings all need to come off. There is a windshield trim removal tool that works wonders sold at just about any Auto Zone or Pep Boys in the country.
The drip rail moulding is very soft and easily damaged. It is removed by pulling the bottom edge out and rolling it up and off of the top edge. Roll the bottom lip off completely before trying to get any of it over the top edge. The best tool I have found is actually a bottle opener to grab the bottom lip but make sure you protect the trim with a soft cloth paper towel or a red shop rag.
The left and right rear lower trim is removed from inside the car. You will need to remove your back seat and the inner quarter trim panels. Pull the headliner down and off of the metal clips to get behind it and you will find 3 studs with nuts. Remove them and it pops off. The headliner can then be removed with a putty knife if it is dryrotted or pulled off if it is still pliable.
MCA 42645, Baton Rouge Mustangers.
1964-1/2 Mustang 260 Conv, 1966 Mustang 289 Coupe, 1975 Mustang II Ghia 302, All projects.....1990 GT Conv triple black driver.
2001 F-150 Lariat for daily use.