Get a spot weld drill bit and start taking your donor apart. As you clean seams and panels, the spot welds will appear. Drill an 1/8" hole in each then hit with the spot weld drill bit. As you take it apart, you will see more clearly what you need to cut and massage into your car.
I actually just buttoned up that area on my car and have moved to replacing the front suspension pan. It's not easy but if you pay attention on how the donor sections come apart, putting yours right will be easier. Take your time and do one panel at a time.
By the way, the guy running the spot welder was a busy man.
