Still a mystery, but now there is one more wondering;
http://www.type34.com/forum/viewtopic.php?showtopic=4539.
This must be the same sunroof, so it's not a one-off. At least a two-off. The manufacturer still remains unknown, as well as the reason why anybody would do such an extensive job when the car could be bought with optional, electric sunroof from the factory.