Barracuda deck panel surface rust suggestions
Mine wasn't quite that bad, but I just got done treating the same area in my 66 Dart a couple months a ago. I won't lie, it was a total pain in the ***. It helps to pull the deck lid, hinge arms, and torsion springs. After I did that, I hit what I could reach with small wire wheels, wire brushes, rolocs, scotchbrite, etc.
It took a ton of elbow grease but between all those, I was able to basically get most of it down to fresh metal. Then I hit it with Phosphoric acid to neutralize what little rust was left, followed by fresh water on a sponge to rinse off the acid. After that, I sprayed everything down with Zero Rust paint. It was some effort, but it turned out great.
Here's a photo of what I started with. I can get an "after" photo tomorrow if you'd like.