One thing to think about,
Was your actual video shot on tape? Camera’s like the Panasonic DVX100 or HVX200 automatically insert pulldowns that make your actual video footage 29.97, even when shooting at 24P.
If you are using 24PN this is a different story.
You can try converting the footage with the wrong frame rates, and then replacing them in the timeline.
Mixing frame rates can make for a real headache.