MM, have you already considered a much simpler solution? The pivot points of body parts in GTA3 work exactly like a bone in VC to which only a single contiguous mesh object with full weights is attached. Back then I considered writing a maxscript that does create a bone and skins VC model out of GTA3 object. swaist object would be tied to pelvis bone, smid to spine, storso to spine1, etc. That is way easier than hacking the entire animation engine. I believe something similar can be done with cutscene models. Then you'd need to write a converter for the GTA3 animations too, replacing the simply the names of parts with the names of bones.
Now of course I don't know what you intend to use all this for *beyond LC* but if it doesn't go beyond the scope of LC, this is a simple, working solution. Afterall the body part system is like a bone system where only weight of 0.0 and 1.0 are allowed. However since this also breaks all original Vice animations I personally decided against it.
About the menu stuff: I would like the user to be able to configure which martial art technique/combo is to be associated with which button or button combo and I want them to be able to do that in an in-game menu at any time.
About the fighting animations:
Well, if the LC project is looking to have original LC actors in-game, then it doesn't make much sense for me to ask for help from people from here in converting GTA3 animations to VC.
Since I have a lively interest in that, it is going to happen anyway though; especially since I have learned that it enables me to use animations from SA and possibly other GTAs very easily.
Should you folks ever change your minds, here's a list of animations that would need to be converted beyond the ones that I have already converted (although that is to some degree prone to subjective impression), you may want to keep that one safely, just in case: (ordered by priority)
Must do for authenticity (animation is fine but doesn't have the GTA3 feel):
HIT_behind (very different animation!)
HIT_R (final stance)
HIT_L (final stance)
Reasonably close to GTA3:
For those last ones and the rest you might want to consider correcting the arm positions across all frames so that they fit with the new fightidle stance.
PS MM, have you ever converted an animation from Vice to GTA3? I know the reverse process isn't too much fun.