If you don't have the old seat pan with which to compare, post a picture of what you have for us to identify.
Many mistakenly believe that a CB550 Four is an F model, simply by looking at the side cover badges. Not so. K models also say Cb550 Four. But, thare are many part differences between them; Seat in particular.
One obvious tell is the tool pouch storage. F models have that pouch stored under the tail of the seat. 75 K models have the tool storage pouch on a tray in the frame up toward the front under the seat.