1968 Dart 2dr post RESTO (father/son)

Supposed to be decent outside this week, so I want to try to finish this k-member. I think today I will finish all the seam welding, and grab some cardboard and make some templates. I can't wait to try what Idaho was saying!

Here is a question. The 3 welded nuts that the box bolts go into have ugly threads. A tap goes in, the bolts tighten up, but they got rusty at some point and there are spots on the threads that flaked off. Should I replace them? If so, whats the best way?