Regarding Rudolf Gantenbrink's CAD "cyber drawings" - yes, they appear to be no longer functional via his cheops.org website.
However - there is a way!
Download the 4x DWF files manually (via inspecting the HTML page source);
Then you can use them with Autodesk's free online-CAD viewer;
Requires a sign-up, but once you're in you can upload the DWF files and they work per