To anyone who read the book...

I read the book recently and there are some differences. Sister Angela is Canadian, not Irish. You find out that Mr Allison's first name is Hank. There are a few scenes, including the ending that are quite different from the movie. If you can find a reasonably priced copy (I paid £18 for mine) it is definitely worth reading.

If you have the patience to read off a screen, both the book and the movie are available on Internet Archive and you can compare them.