To cut the steerer tube just use a hacksaw and cut it about and 1.5cm under the top of the stem. As for the headset just use a mallet to tap it in, then tightening the top cap bolt will do the rest of the job.
Indeed looks really modern and futurist for a trials bike. Where did you find these pictures? Edit: www.observedtrials.net and I heard that yes the sky range were going to be like that. Can we preorder them from you adam?