I don't see much rust, let alone anywhere where I would be worried about replacing things. If it is worrying you too much, I agree with Russ on this, just replace both panels. I tried to separate the top cowl panel from the bottom, and it didn't go well. I wasted hours trying to do it, and ended up just having to replace both. If there is just some pin holes, I would just plug them up with weld and grind it smooth. It is a fine body to start with from what I can see, much better than this:
-Mr. Moe-par
1968 Road Runner, 1968 Coronet, 1968 Coronet, 1969 Dart