Couple issues on my new to me 65 dart…
I had rust issues in my cowl too. Both fresh air openings into the car were rotted out and holes in the cowl in the engine compartment. I don't have the skills to take the air box apart, so I did the best I could looking for holes with a light and grinding / sanding as much rust as I could reach. All my holes were on the outside ends of the cowl box, so I could clean them up pretty good by hand. I used POR15 with the fiberglass mesh and the POR hole filling paste to repair the holes. A buddy with welding skills welded in new tubes that the interior fresh air boxes attach to. Then I taped off the cowl's intake grill and interior openings and flooded the dog crap out of the cowl box with Eastwood Interior Frame Coating (fogger). I put so much of that stuff inside the cowl, it was flowing out the outside corner water drain holes and puddling on the garage floor. I checked coverage inside the cowl with a bore camera and l QC'd my hole patching with a light. People with a more advanced skill set would have done better, but this is the best I could do with what I've got. And it doesn't leak for now...
I had rust issues in my cowl too. Both fresh air openings into the car were rotted out and holes in the cowl in the engine compartment. I don't have the skills to take the air box apart, so I did the best I could looking for holes with a light and grinding / sanding as much rust as I could reach. All my holes were on the outside ends of the cowl box, so I could clean them up pretty good by hand. I used POR15 with the fiberglass mesh and the POR hole filling paste to repair the holes. A buddy with welding skills welded in new tubes that the interior fresh air boxes attach to. Then I taped off the cowl's intake grill and interior openings and flooded the dog crap out of the cowl box with Eastwood Interior Frame Coating (fogger). I put so much of that stuff inside the cowl, it was flowing out the outside corner water drain holes and puddling on the garage floor. I checked coverage inside the cowl with a bore camera and l QC'd my hole patching with a light. People with a more advanced skill set would have done better, but this is the best I could do with what I've got. And it doesn't leak for now...