Tim, here is your answer from a Mustang article that Paragon posted in the second thread I posted. Did that make sense? Anyway, here is the link complete with pics.
http://www.mustangworld.com/ourpics/fcar/antenna1.htm
Remove the antenna from the car. To remove the tip, I clamped the antenna to a workbench and fit it into the notch of a nail puller (wrapped in some electrical tape to reduce nicks). The tip easily popped off with a couple whacks from a hammer. (Careful not to lose the tip. It's small and will go flying!)
Decide the length you want to cut the antenna down to. I went with 18" from the bottom, which makes it about even with the top of the roof. You could probably go as short as 17" or so, depending on the result you want. Measure carefully and cut with a hacksaw. Lightly sand or file down the cut end of the now shorter antenna to make reapplying the tip easier. Put a small amount of strong adhesive inside the original tip and place it back
onto the antenna. Make sure the tip is sitting straight before the adhesive dries.