The man at the Controle Technique (= MoT) complained that my headlights couldn't be adjusted high enough. That is to say, I wasn't able to dazzle oncoming drivers.

The adjustment is all the way "up", so I'd suspect he's right. I very seldom drive it at night, so first-hand experience isn't much help.

I've never touched the adjustment system. Is there some known way of packing the mechanism out, or shortening something to make the lights go higher?

Or do I have to attack those two big rusty nuts under the headlight shells to set the lights higher in relation to the headlight bar?

Advice would be very helpful. I'm getting out the WD40 right now....

There's a degree of adjustment via the 19mm nut securing the headlamp bowl to the bar. Just a case of loosening the nut and moving the bowl.