When I tighten the headset, it doesn't rub with the frame. There's actually a few millimeters between the headset and the frame. I've had that issue you mentioned with my previous Velobuild and I fixed with the same type of thin spacers.
The problem now seems like no matter how much I tighten the headset, there's some play in the steering when braking. And if I keep tightning it up, the compression plug slips up.
So I guess that's not a common occurrence for this bike? hm, I'll keep investigating what could be the issue.
Still having issues with the vb-168... Went as far to file down the "tabs" on the original (new style) c-ring, using a 2" compression plug and adding 4, 0.25mm micro spacers, still had substantial headset play. Currently awaiting new Deda 270° c-ring to verify if this will work
Update:
The new 270° round Deda c-ring work. I tried both, the Deda 36° and 45° angle. Both work.
The original VB half-ring was ~1.12cm wide and had quite a gap between the head tube and headset assembly.
I reduced the Deda by 3.76mm and sanded til smooth. Since the Deda were plastic I used 1, 0.25mm micro spacer as a protective layer. Now there are no gaps and the assembly is flush.