A question that I have already asked and they've assured me that the engine that was donated was exactly the same as the one that it replaced and had done 60k miles. They have also said that it will come with a 12 month warranty. My experience of warranties isn't the best so I'm more concerned about what people's feelings are about buying a motor with a reconditioned engine in it.
I guess if it's been done properly then there's no issues however that might not be something I find out until further down the line. On the flip side I could buy with the original engine and it goes bang in 6 months time anyway so you never really know!!