First of all I would like to welcome you to the bolt. You will meet lots of great people here.
It it was my truck, I would not use the trailing arms that are rusted through. That is part of your rear suspension, and to me, it could be a saftety issue. I am not aware of any venders that have them, but you might be able to find some used ones off of another truck. Good luck with your project.
Jim
