Trial and error. I've searched and searched, and nobody has ever ripped the data from it.
I also know absolutely nothing about ripping data from 64, or I'd do it like that.
Hitbox sizes will be done by doing the whole "making hitboxes visible" technique, and comparing them to the 64 ones done by Fireblaster. A slight problem could arise, as afaik hitboxes were actual boxes in 64, and in Brawl they're more of a bubble. Probably won't be noticeable.
Right now I'm dealing with a load of school ****, though. So work is slow. Practically nonexistent slow. Mostly I'm trying to find the necessary codes to make this happen, and familiarizing myself with some of the more intricate mechanics of 64.