What year? If it's '69ish or later (car), it should have the dual-pattern bellhousing, used with both transmissions. Earlier bells were trans specific.
Slide under the car and take a look. Even with a trans in place you should be able to see the other pattern showing on the bellhousing.
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My only concern is that the retainer hole matches the diameter of your particular four speed, they varied by year and original application.
Edit: I see now you said Duster in the thread title- so it should be the dual-pattern bell.
