I cannot disagree with Erik as I use only a hydraulic damper. When I designed my new steering stem I made it as a direct replacement of the original. It uses the same bearings, spindles, and all of the original parts, including the steering damper. I did that because I believed that most owners would demand it.
I would note for those who are not familiar with the steering damper that the 'D" and 'C' dampers are different ( the 'D' having two friction discs) and they are not necessarily interchangeable. They may be interchangeable based on the length of the stem's protrusion from underneath the assembly.
In fact, I did not bother with the friction damper on the taper roller steering stem I made.
I used this stem on the racers that had hydraulic dampers. The stem itself is metric, which allowed me to run metric taper rollers.
I think Norman is providing a real benefit to Vincent owners and I hope that those who have an interest take advantage of his services.
David