Thanks for the help but are you sure that applies to a 1987? All the auto parts websites list one for that year. Rockauto, Advance, Autozone, and O'Reilly list a Four Seasons 74612, and Napa lists one under their own part number that looks exactly the same.
I looked in my Haynes manual and it doesn't talk about one, which supports your position. Also, I looked under the hood of a friend's 1988 GW and it also doesn't have one, again supporting your position.
I'll be very happy if I don't need one because it saves me time and money, makes the heating system simpler, and reduces the potential for leaks.