Hi
I don't have the official term for you, nor did that part number yield anything on the y2kford.com site, but I would call it the heater outlet pipe. It is about 3/4" correct? And held down by a single small bolt on a tab? On the end as you remove it there are two o-rings that complete the seal. Whatever it is called I believe you will need to go to the Ford counter. Your local parts folks should be easily able to pull up the number for you and can print out a diagram of the water pump and associated assemblies.