I bought an 07 YZ450 the other day for the forks. It's complete, and not in bad shape except for the head which is off and gone. There is a very slight mark on the piston where one of the valves hit but I don't think it's enough to have done any damage. Everything on the bottom end seems fine but I'd pull it apart before I spent any money. I bought it without a title but after talking to DMV I think I can get the title without much if any back reg. Just guessing I'd say it has 75-100 hours on it. I paid $700 so I might be able to get it going for another 8 if I patiently watch Ebay.
Should I
"A" do my original plan, take what I want for my YZ, and part it out.
"B" find a used head and put it back together, I don't have a 450 and would love to have one again for longer off road stuff, I'm about 10 years past caring if I have a new bike or a good 10 year old one.
Or
"C", swap the forks with my 03 YZ, sell the engine, carb, and electronics and put in an XR200 engine I've been building for just such a rolling chassis for a bike to follow my 7 year old around the woods.