Looks like a problem: you'll probably need more threading on the steerer to use any common headset and so will allow the threaded top cup to engage. The top nut is least of your problems and if you hate spacers you could cut off excess (threaded) steerer but you don't have "excess", IMO. Getting threading added USED to be a relatively "routine" job for a well-fitted and experienced shop, but nowadays not so! Depends on your location and luck. Always BEST if you can find somebody with a lathe and experienced in cutting threads that way, generally better threads than with a die. Even HARDER to find that! Good luck to you, I have been down this road several times and feel the pain!