You don't need to take off the bumper. You will have to drill out the factory spot welds on top and under the car along the quarter panel seam. I would pull the tail light to make life easier. But overall it's a pretty easy job. Use a 4" grinder with cutoff wheel and get the major part cut out. Then drill out the spot welds around perimeter. Use a hammer and chisel to separate the seams or an air hammer with chisel bit if you have one. You can look back through my build thread and look where I did the trunk. Let me know if you have any other questions.
https://www.7173mustangs.com/thread-new-project-for-this-winter-71-mach-1
That's where I'm confused. When you say top do you mean inside the trunk? Does taking the tail light off help access the top area from inside? The guy that owned the car before monkeyed every repair you can think of. That trunk extension section... he installed an old sign caulked into that area after taking most of the drop off or extension out. It looks like he got most of the metal off but the top section close to the tail light is still in there. Trying to figure out how to get that section out. Cant access from underneath.
Thanks for Your Help,
Darren
Ok.. I just went out there in the garage after looking at your pics. The guy covered the whole car with tar and its so hard to see where things start and end. Just scraped the tar off and it looks like the top of the drop off 90's under the trunk floor. I see what your saying about accessing the top. Makes sense. I can feel the 90 under the trunk floor and where he left the rest of the metal from the trunk area. Once I clean up the area a little better I will see some of the welds through the trunk floor. Am I heading in the right direction?
Thanks for Your Help,
Darren