I think that's impossible (or at the very least illegal and time consuming) because:
1. JKII uses the Ghoul 2 model system, with skeletal deformation, instead of Q3A model deformation. You would need to "rewire" the models completely, and if you've seen the number of animations the JKII models use, you'll know it's damn near impossible.
2. All Q3A models, maps, and skins are owned my Id, and it would be illegal to distribute their models and skins for free.
I know this because I wanted to convert Xaero to JKII. (Tibetan monk cyborg with a lightsaber...

) For some decent skins and models, just go to
http://www.jediknightii.net .