I would not recommend using a threadless headset if the top race contacts the steerer tube in the threaded portion.
The tube may be weaker in the threaded area, creating a stress point where steerer exits the tapered collar.
The threaded portion of the steerer is typically reinforced by the threads of the threaded top race
on the outside and the quill stem on the inside. That moves the stress point inside the steerer below the top portion of the headset (inside the head tube of the frame.
What type of stem arrangement wold you use?

Possibly the more learned minds will have other opinions ??