If you have FinalBIG, extract all the parts of the command center (a1,a2 etc.), the game has a different model for each animation (e.g. the US CC radar dish has slower animation that the fans' one, so they're separate models).
I'm not sure how C&C 3 works, but since in on the same engine, I assume it's gonna be based on something similar, so you could just import the files into the directory and code them.
As for the rigs, you have separate files for skins/models (_SKN) and rigs (_SKL) with additional animation files (e.g. _RNA) and they all cooperate through code e.g.:
Model = AIHERO_SKN *Model file
IdleAnimation = AIHERO_SKL.AIHERO_STA 0 25 *Rig file.Animation file
But, I've never modded C&C 3, so that's just theory