i have a '71 convertible that was originally a new york car and has the expected sheet metal rust. the frame rails, torque boxes, etc. are in good shape, though. my main concern is the rust that is falling from behind the dash into the passenger side floorboard. the passenger side floorpans are also rusty, indicating water is leaking through the cowl and onto the floorboard. how difficult is a cowl replacement on a '71? i know it is a major job on prior years, but i've never seen much on the '71-3's. could that rust be coming from anything else? thanks.