The K I recall stands for keel, they are positioned on the bottom corner of either side of the part of the fuselage that slopes up towards the tail.
It is a long time since I flew the 228k but I believe with the keel you get an increase in take off weight.
Looking at pictures of G-SAYE the keel's are not present, google G-MAFI and you will be able to compare with an aircraft that has them fitted.
They may have removed the keel as they do not need the aircraft to operate at the increased weight and having a lower take off weight might bring reduced landing and navigation charges