The area of rust you are dealing with tells me that water has found a way inside the roof somewhere. Carefully inspect the roof for any holes where the roof meets the drip rail.
I am not an expert on body panel repair. However, I have looked at enough of these trucks to know that rust in that area can be more extensive than what is evident on first inspection.
For me, the biggest obstacle to getting it done is overcoming the fear that I will fail. If you can shape metal and have a decent welder and a few simple tools, then I am sure you will be able to get it done. Take lots of pictures and pay attention to compound curves.
