I've googled Cees Boer, mailed them with a link to this topic, maybe they can enlighten me.

Detail, whilst looking at their info-page I saw this pic:

If you look at the window in the back you see the name Cornelo, which has more than once been named as a dutch framebuilder whose High-Quality raceframes look a bit like colnagos.
Maybe that's the real brand, and (one of the) later owner (s) repainted and "rebranded" it.
Also googled and mailed Cornelo - the kokke-bikestore (cornelo site seems to be defunct).
Let's hope for some results.

Seems I have solved the Zeus-fork mystery myself, they sold fork crowns to framembuilders:
http://www.classicrendezvous.com/Spa..._frm_parts.htm