As I said it does not mention much, there was a documentary about the 777 and had a section about what Boeing went through to get her to fly again to be an engine test bed as she was the only 747 owned by Boeing and it was cheaper modifying the prototype than renting a 747 and converting it.

There is a bit about it on here

http://youtu.be/th5gyTvuxE0

Curlyboy