answered my own question – here is one way to do it:
the anamorphic check box is simply telling FCP to change the aspect ratio by -33.33
1.if you double click on a clip in the sequence, it will load it into the viewer. Under the motion tab, twirl down the aspect ratio category, and change the -33.33 to 0
2. Make sure the clip is still selected and hit apple-c to copy this attribute.
3 select all clips in the sequence you want to change and from the edit drop down menu choose “paste attributes” and choose “distort” from the dialogue box that comes up.
This has stumped me for years – if you know of a simpler way, please let me know. (nesting a 4:3 sequence in an anamorphic sequence does not work as far as I can tell)
Mike O