I'm wondering the same thing but the other way around.... 550K fitment onto a 550F?  
One of the prior owners of my bike messed up the drive assembly cable connection on my bike.  
Now if they don't fit, and you have one for a 550F and I can get one from a 550K then maybe we can make a trade.  A buddy told me he's got a parts bike in his backyard and is pretty sure it is a 550K. 
Pat at APE