"In this Final Cut Pro video tutorial, Creative Cow Leader Shane Ross discusses taking 60p footage shot with DVCPRO HD and slowing it down to 23.98 so that it's slow motion. Please note that this only works if you are working in a 23.98 or 29.97 timeline."
Also - you might check to see if you have anything like "Removed Advanced Pulldown" checked when you ingest, it would explain why your 60p footage is landing in FCP as 24p.
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Video Photographer / Avid & Final Cut Editor