Has anyone ever replaced or repaired the box structures that hold the metal rear bumper? On mine the mounting ears are bent and one is smooshed a little. My guess is that these *do not* get straightened but need to be replaced. I have located 4 Fieros in junk yards close, so I have a good shot at being able to cut these off and welding new ones on. Guessing that is how the originals are done.

So, anyone ever done this before?

Smooshed how much. With proper tools they can be pulled out. I used metal sheet lifters, a chain and my garden tractor to pull the crush structure back out on an 86 years ago.
The bumper mounts are easily reformed with hand tools......

The mounting flanges can be straightened without any ill side effects.