Mine was missing. I topped off the coolant below the overflow hole. Covered the area with a damp towel. Just like a water piper, solder and heat. I used the wrong black paint but it's not a show truck.
You probably know this but there is an original overflow recovery option but parts are hard to find.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
