Torque Boxes?

RestoRicks are pretty correct in looks/design. That's why they are expensive. Like anything restoration oriented.

The auto rust technicians are workable, but, not correct looking.

I agree with stroked on this point, if you are going to upgrade the chassis, go frame connectors first. Better bang for the buck.

You could make a set of rear torque boxes for under $20 if you have even basic metal working skills. All the basically do is triangulate, boxe the forward edge of the rear spring perch mount. If you don't want pretty, they are simple to make.