Depends on what pipes you have. If you have a 4/1 you can fit the F version if you have the 4/4 originals for 550K1 then you'll need the early 500/550 with the long arm. My experience is that the 550F version is better as the arm is shorter, but more tightly angled and find it better for getting on the stand. But as I said before I am a weakling.
The later F2 (short arm for 4/1) and then K3 (long arm for 4/4) were different looking construction, but may also fit. Anyone tried?