All you needed was one of these to convert to a modern threadless stem. But if you wanted a new threadless fork then getting a new top 1-1/8" threadless cone and the proper spacers, as well as a star-fangled nut, threadless bolt and top cap would be at minimum as Kimmo said above.

Just don't ever try and clamp a threadless stem onto a threaded steer tube on the threaded portion. That's a recipe for disaster.