One thing I'm wondering - if I do that, should I offer two versions, one with and one without the book. Can't really justify charging more for it, since it's public domain, but some people won't want the extra download etc.
Later: Just finished pasting it in formatted to the right size etc. Looks like it'll add 40 pages, won't know for sure until I've finished editing it. Still worth having, I think. In accordance with what people have said I won't offer two versions.