I had to cut about 30,000 words from my thesis. I just wrote the entire thing, knowing I was going over the limit. I planned to cut down at the very end, and so wasn't bothered a whole lot about the overall word count as I went--trying to stick close to what I was supposed to do, but not stressing when it started to go over. Its easier to cut than to write, I think. Well at least for me. I binned some of my favourite arguments, but they had to go, as they were not adding to the main line of thinking. I ended up with a much more streamlined argument and clear focus. So if you write another 30,000 words ( 15k per chapter) you will be just exactly where I was. A day at the keyboard with the delete key whacked it all down, no problems. Just write. Worry about cutting once its all written, then its more obvious what needs to go. At least that was my experience. Good luck!