We appologize for the breaking changes in the Q3 release - we had good reasons for them and I hope you will be able to benefit from the result of the changes, despite the overhead of adjusting your code to them.
Regarding the RadBook control, in order to use it you need to reference latest versions of the Telerik.Windows.Controls.dll
binaries. Whether this is feasible depends on the structure of your application - if it's comprised of loosely coupled components and you need to use the RadBook control in a single or isolated subset of the components (which do not depend on the older version of the same two binaries), then there should be no problem. However, using the control in a project/scope that references controls from the old version of the assemblies would not be possible.
I hope I was able to help. Please accept my appologies for any problems you have because of the breaking changes in the Q3 release.
the Telerik team