What's the best way to get into the cowl in front of the windhield where all kinds of debris collects and eventually starts to rust?

 

On my 1980, you just take the screws out.

 

Plasma Cutter, Holesaw, Torch....

There are some plugs on my 77 that allow yu to flush out some of the bigger items that have "grown" in there. I had the unfortunate luck of having the cowl area rust out in a couple of places due to stuff building up in there & staying wet. I had to pull the dash out to fix it from the back side. But, that just gave me the excuse to finish off the dash in a custom project by removing the pad, welding up all the holes and then body working the result. It will be painted when finished, maybe some old school striping as well, but it is definately custom !!!