Alex,
It consists of a standard skf double row roller bearing, mounted on top. On the bottom, there is a conical inside bearing, the outside ring for that is special, it's selfmade with the center out of center. I had such a set for 40.000 km, then the bottom ring was at it's end. I can send you a picture if you like. I think it's worth it. You get one degree steeper headangle, and so also 15mm less wheelbase.
I have, after 9 years opted for the dynotec frame mod, now I have two degrees steeper, and a wheelbase of 1430mm. That's 450 euro. But they are busy, so if you want that wait till the winter.
Normal steering head bearings are 5 euro at the bearing shop. it's 52x25x 16.25 mm conical. Can't remember the number.
So all options are here, only there is also the deas solution, but to expensive.
And to make it complete, a triple clampset with shorther offset is nice. ( as the WP clamps I still have)