1. Nobody really knows how the scaling's gonna change. The best thing to do seems to be to scale the Halo 2 model, get the physical dimensions, and then scale the Halo 3 model to match those dimensions.
2. If you bothered to read the other posts in the thread, he's working on it. To be honest, if you're in a rush, not many people will notice if you wear a Halo 2 helmet with Halo 3 armor. That's what I plan on doing for Halloween, unless the armor progresses faster than expected.