The steering stems that I have seen have always been pressed into the lower clamp from the bottom, and they have a lip to create a positive stop. The only ones that are different are the billet KTM clamps that allow you to pull out the stem by hand, when you flip it by 180° you can change the offset as they are concentric.
Just like on these I think you should thread the bottom of the stem for a large M20 1.5 bolt like you have on top, to prevent the stem from ever popping out of the hole because you just have a press fit and no other means of retention. Even just tightening the steering bearings you are putting a pulling force on it otherwise.
By the way I recently bought a slightly bent 690 Enduro frame, just missing the headstock as that has to be sent in to KTM if you want a replacement. Thinking about having a pro join that up with the stem from my old 640 frame and somehow make the Versys engine fit in the middle, à la Mr. Quacamole.