[phill168]

I guess I must be the only person on the planet still using SDII.

Well, I managed to find my old manual and found the answer. If anyone's interested, here's how to display the waveform in the overview:

From the manual:
To choose between the waveform display and the time line display, hold down the option key while the mouse cursor is over the overview area. A pop-up menu will appear. Keep the option key down and click-and-drag the mouse to select either Time Line, or a channel to view. Notice that stereo files also let you view a composite of the left and right channels at once. The option key pop-up menu just described in the only way to select what will be displayed in the overview.