You can do the same thing with X0 footage: AssumeFPS(23.976) or AssumeFPS(25) will make it line up with your existing IVTC'ed NTSC source, or your PAL source.
The point (for me, anyway) is to get all the frames labelled with a unique, 24 fps timecode number. Once that's the same as the X0 Project, then laying in new audio at either 23.976 or 25 fps shouldn't be tough.