'63 valiant 4 door /6 cruiser questions.

Head work wont hurt what you do later. Cam depends on what year cam was used as there are a few.
The cowl has external vents that allow water to fill up and come through the fresh air vents. What is supposed to happen is the water is to drain out between the fender and cowl. But the debris collects in that seam and the only way the water can get out is through the fresh air vent. Put a water hose in the cowl and watch....
Frank