the only way to really fix the rust in there is to cut the cowl open and replace the metal. i need to do this but im going to practice welding my floor pans first, since those wont be seen when the carpet is in. how bad is the rust. if its just surface rust, you could blow the dirt out with compressed air. i did this for about a half hour. i had tons of pine needls in there. the debris will blow out the sides by your fenders . when you open the front doors you will see everything gathered up in the bottom of the fender. after i felt it was pretty clean in there i sprayed por-15 metal prep in there through the fresh air duct holes, cowl vent holes ( pull out the rubber plugs to gain access), and the top cowl vent.then i rinsed real well with water.after that i let it dry out for a few days and the applied por-15 paint inside as best i could. this is just temporary untill im brave enought to pull the windshield again and start cutting. if you have welding skills i would go this route and just get it done, and done right. good luck!
