I have a 99 YZ400F that I was planning on doing a full engine rebuild on. A friend of a friend has a pristine '07 YZ250F chasis that he would sell me for a steal. It is totally complete minus engine. I got to thinking would the 400 motor fit and would it be a worthwhile swap. My 400 isn't my primary bike anymore so I could take my time. Has anyone ever done something like this?