If you buy the stock from Ford, it comes with the housing and water pump (the impellar is with the pump). From what I read, 99% of the time it is just the WP which is the problem. You probably don't need to spend extra money or time to replace the housing and hoses.
Most autoparts stores sell the water pump only.
From my experience, Autozone and Advanced Auto sells the black impellars only (eventhough Autozone can special order a white one or metal one for you). Napa has the white impellar WPs in stock at its stores and can order the metal one for you too. You want to get the white impellar or metal impellar ones. Oh and when I was at Autozone and Advance, the reps there said, "Yes, we have the metal ones." Turns out, they are talking about the pump and not the impellar. If you are not sure, open the box before you buy it. Oh yes, and at one store, the rep, kept insisting there is no impellar in a water pump. When pointed out to him, he said, "Oh, you mean the propeller"
Edit. One other thing. You may want to install a new WP belt also (about $12).
