The .h264 will not help.
Use the mpeg preset.
You will likely have stuttering movement with 24p. Nature of the beast. You have to look at what you have and work with it. You have 25p and you want NTSC. The best option is 24p. Now I have put 720p/25 material in a 720p/60 sequence with out issues… I ahve also used 24p in a 60i sequence without issue.
There is probably not much more you can do here but accept.
You can make a copy of the 25p clip(s) and open them in Cinema Tools (comes with FCP) and do a convert to 24p before the edit, but I don’t think you’ll see a dif here.
Chris Tompkins
Video Atlanta LLC