One of the first things I wanted to do after getting the car starting and stopping like it suppose to was to address the cowl leak. I removed the heater and driver side fresh air vent to evaluate the problem. I could not get over the amount of leaves and trash stuffed inside the cowl. After removing a small bag of leaves by hand and using a shop vac I thought I had about 90% of the leaves removed, wrong...only got 50%, if that much. After driving a block or two down the road I turned around to head back home to vacuum more leaves. I did this 3 more times before blowing compressed air around the vent chimneys. I expected to find a rusted out cowl but I found only one 1/4" hole. I hit the rust with a wire wheel and painted on a couple good coats of Rust Bullet and Por15 putty took care of the rest of the problem. This sure beat removing the windshield and drill out spot welds to remove the cowl to get to the area for repair. Most likely water was wicking up through the debris to overflow inside the vents or the leaves slowed the water enough that it could not drain fast enough.
While the heater was out I decided to rebuild the heater box and replace the heater core. To my surprise the Ford part number was still visible on the heater hoses with the original tower clamps and the heater core never has been replaced. The heater box had a broken corner around the cowl opening. I used Permatex epoxy to glue the piece back together and sanded down the glue with a Dremel. The driver side vent cable was broken so I made another mount from thin angle stock and an aftermarket choke cable.
Jumping ahead a few month later...I removed the lower dash and installed a package tray from an early 71 Grabber. I swapped to an early style heater box that used a door. This heater box was broken also and was repaired with Permatex epoxy and reinforced with metal (tin license plate) on the inside of the box. The plastic rivets holding the register broke when I tried to remove them so I used small machine screws to replace the rivets. I used the Dremel to file extra clearance on the door to clear the nuts.