I have a spare 2008 600 engine that I received with the purchase of a new-to-me used bike. I have no first-hand knowledge of its condition. The seller who, I believe, also had received this spare engine from the original owner, told me it "has two bad valves". What exactly that means, I don't know. I wrote about it in this thread. I don't have the skills or the inclination to dig into it and find out what exactly is going on. However, if you do, I'd be willing to make a very reasonable deal for it, including delivery to Milwaukee / Madison latitudes (I'm in central WI). PM me if interested. I can provide photos, as well.
06-24 engine is what you need. if you get 06/07, you'll need an 08+ temperature sensor and throttle body gaskets that bolt onto the head. this should help your search.