just a quick check here:
SD can be presented as 16/9, too, if you go anamorphic.
are you committed t a 4/3 presentation for some reason?
in FCP7's title safe overlay you now get 4/3 marks as well to help with this.
if you are on a lower version you should look into Digital Heaven's "Guide" generator.
this can sit on a higher track give you custom guides.
set the left & right guides to -60 & 60 to define title safe,
and -68 & 68 to define action safe.
(i just got those figures by matching them to the title safe marks in FCP7)
cheers,
nick