I have a 500T triple tree on a 550K1 and haven't had any issues. The steering stems appear to be the same; I used an All Balls tapered bearing kit and it dropped right in. The mount for the brake junction is a little different but the junction block will bolt right on. You'll lose the steering lock, if that matters, and the 500T top clamp has a mount for the ignition lock which you may or may not need. I cut it off and smoothed it out since the stock ignition lock for the K1 is under the tank. I don't know if the stock headlight ears will work because I omitted them and went with aluminum ears. And the instrument mounts are different.
Good Luck,
~john