I just stick with stang stuff, just to keep it simple in my head, and not confuse myself. Make sense?
I think if you get the other water pump, you'll be good to go. Maybe the van had the HD cooling, and came with a bigger pump?
Most of the pumps you find are going to have the correct mounting points for the brackets, I think I know ZACKLY where you're talking about, been there!

Try the water pump first bro!