Got it registered!!!
One month before Brexit, after which it would become practically impossible to register. Took me three attempts in total:

1. Went to the RDW (Dutch equivalent to DLVA), when a injection lead broke for my Transit towing van, spilling diesel all over the road.
2. Next try: the RDW wanted to have full lighting, mirrors and catalysts mounted before registration. Besides, they needed an official declaration of engine specs.
3. Sailed through in the final attempt. They did not even look at the catalysts I struggled to integrate into the exhaust system (Cologne V6 needs two of them)! Had a good side too: they did not check the lighting E-marks, which was kinda lucky as the indicator lenses had none (as Dino NOS).

So now it's of into the garage until the house build has finished.

Ciao, Kai