The joy of used parts. You stare intently at pics online, or on ebay, read and re-read the seller's descriptions until you have them memorized, and then, hoping for the best, pull the trigger and an electronic financial transaction takes place. You wait a few weeks, pick up your wares, and hope for the best.
I've done OK in the past with used engines. Although this has turned out to be dud #2 (the first being a KTM 450 engine for another supermono project years ago). My plan was always to rebuild this engine, as while it was complete and advertised as a runner, mounting up the engine as a empty case in the frame is a lot easier weight-wise. And I wanted to inspect the lump in detail anyway. TT/XT 600 engines are pretty simple to take apart, with the only issue being a universally stubborn rotor removal. I set about the dissasembly, going as far as getting the rotor nut off (with heat and an impact gun), and then flipped the engine over to remove the clutch side components.
With my OCD tendencies when it comes to engines, this is now for parts only. I've opened c claim to get back some of what I paid for (admittedly cheap, but still). The search is on for another engine in the mean time.