Cowl Inspection and Cleaning
The cowl assembly on these old Mustangs is a known trouble spot. Ford didn't do much in the way of corrosion protection, nor did they design the cowl to allow easy access for cleaning after the car left the factory.
Over time, the cowl would fill up with leaves, pine needles, and other debris while the car sat parked outside under trees. In many cases, mice would build nests in the cowl of cars waiting to be restored "some day". Rain water would get in there, quietly and invisibly soaking the stuff in the cowl, and eventually cause the cowl metal to rot away. The rotted cowl now allows the same water to get into the car and start rotting away the floors.
Instead of a well primed, sealed and painted cowl from day one, you get to replace floors and other metal decades later. Or not, depending on how lucky you are with your particular car.
My car needed a small patch on the passenger side toe-board. I was worried this meant my cowl was rotted out and would need to be replaced. The cowl is a two-piece affair, top and bottom, held together by a gazillion (~200) spot welds and locates the base of the windshield, the export brace, and centers the rear of the fenders. It's visible and it's structural, so it's pretty important to make sure it's in good shape.
First thing I did was determine how bad my particular nightmare was. Once the fenders were off the car I used compressed air to blow out the cowl and fished around with a hanger to pull big bits of junk out though the drain holes on the ends of the cowl.