The solution and project have been updated to MVC5, and Web API 2. In addition, editing PowerPoint (PPTX), and Excel files has been added. Word Editing is not part of the solution. Also, PDF viewing is enabled.
The latest Solution and information is up on Code.MSDN:
http://code.msdn.microsoft.com/Building-an-Office-Web-f98650d6
And also here: http://cicoria.com/downloads/CL-OwaWopiNetFx45MVC520140131.zip
The old post is here:
http://blogs.msdn.com/b/scicoria/archive/2013/07/22/building-an-office-web-apps-owa-wopi-host.aspx