James,
If you plan to keep the trac for a long time more, I would go with the rebuilt. Keep in mind though, at 200K miles, the Engine may need some attention, or even rebuilt before long, as nothing runs forever.
If you intend to trade or sell your Trac in the next year or so, you might consider the used, as long as it comes with some guarantee... (On used major parts, I usually want a 90 day replacement guarantee at least, that way if it fails in 60 days, I can get another one from the salvage yard) Still have to do the labor again though.
My $.02 ..