I'm almost certain that neck cranks of all sorts were and are legal. If the twister is perfectly legal I don't know why that wouldn't be.You are also not allowed to grab the head and chin and twist.
This? http://www.youtube.com/watch?v=44E-lW3aYhM#t=1m02sAaand you are not allowed to clap your hands together over one or both ears.
The thing the gracies did in the early UFC days was a two fold approach....they purposely had Royce fight Art (the boxer) in the first ever fight, and the refused to include high level wrestlers until UFC 4 (severn) because Royce wasn't very good and they knew he would probably lose - even though he beat Severn at 4.All of these will pretty much put paid to such an attack. Gracie knew it and so made rules that would benefit the kind of attacks he could win with. You can argue that they are there for safety and that's true enough, but let's not overlook the self serving aspect too. That's why he did so well for so long.