Many parts are interchangeable on the frame and forks etc.
Side panels are different, and chain guard, rear mudguard, tank, seat, clocks, headlight, and exhaust obviously is a 4 into 1 on an F.Engine is different but will fit from a K to an F. Sounds like you want a K, I have an F and love it, but I would still prefer a K with 4 into 4..
Jim.