Looks quiet complicate. Does your final DVD has to be in NTSC? I do not know too much about that, for I am living in PAL land.
I assume, that your original timeline with the EX1 Footage is in the XDCAM Codec?
If yes, I would first export the whole project as QT with Apple ProRes HQ Codec.
Put that one into the Compressor. Drop the 90min Highest Quality setting on it. Make sure you set the “Dialog Normalization” to -31dBFS and set the “preprocessing / Compression Preset” to “None” (Both are in the Audio Adjustments of the Inspector.
At what point during this process you switch the frame rate to NTSC – I would not know – as I said, I am not from the NTSC Planet. But I would take a wild guess: Do the frame rate conversation after you rendered into ProRes, back in FCP – with Nattress or something like that.
Sascha