The forks with the longer steerer tube can be run 1 Inch Threadless.

Otherwise you're going to want a 1 Inch Threaded Headset (26.4 Crown Race) with a Quill Stem.

Edit: My white 50cm kilo frame arrived very fast! Props to Jeff and some great customer service over at Bike Island! It looks like it's going to make a great worry-free city bike!