ok, that's not the configuration shown in the article you linked, as far as I can tell. Those bikes both had DF-style forks in a traditional steerer tube. I believe you will have to have that fabricated, although you could use a 44mm head tube and a fabricated "steerer." The tapered steerer that Pargon makes would be something to look at, they do have drawings. You would want a more symmetric design. 44mm forks have more of a cantilevered load than mid-bike steering does.