69 kick panel/vent structure rust

[Tower's Trucks]

I have a major rust issue. The truck is a beautiful big block automatic with wood bed and P/S that I want to save but this may change my plans. The driver's side kick panel has a lot of rust, and the bottom of the vent opening where the vent door rotates has all rusted away.
It appears that the vent structure that is spot welded to the outside of the "A" pillar filled up with dirt and rusted. This in turn rusted the kick panel.
I don't see replacement panels for it. I'm likely going to have to find a donor truck, but it looks like a huge job. Has anyone tackled this and do you have any advice?
Thanks!