I am working on a '69 Camaro right now and have a rust that is severe at the windshield are that has required removing part of the front dash area and part of the cowl under the dash, luckily I can retain the original part of the cowl that has the hidden VIN numbers and my cowl tag, so I have ordered a repro dash panel and cowl and then carefully cut out the bad areas in the dash panel and cowl and butt welding in only the areas that needed to be replaced thus saving the important VIN, trim tag and hidden VIN on the cowl, it's a lot of work but I feel the best way to restore the car.