I hope these answers to your comment about the 4 gospels may be of interest to you....
The end papers were printed some time ago, standard leather jointed etc. The end paper design is derived from the text. There will be direct links to the outside of the book and the endpapers.
I hope that each book will stand on its own... as a single design binding and within the group of 4. It will not be easy but life would be boring if I did the easy all the time.
The construction is the key to the whole project (as you have pointed out) I hope that the construction will be flexible enough to cope with the various differences in the board thickness from one book to the next, from one board to the other.
One of the problems of doing a design binding is the fact that it is seen from a distance and close up, when one is reading the book you are very close. I feel the design must be not just the image the creation of a 'Texture' for the eye but also it can have a physical texture.
The nature of the book is complex, in a recent lecture I said that the book is an amalgamation of so many different materials, rationalisations, methods of production, history etc etc..... I just seem to be doing most of it on the 4 Gospels!