Well, the CB500T is a 2-cylinder 4 stroke TWIN.
The CB500K and CB500F are SOHC 4-cylinders.
The difference between F and K models is a little more subtle, I am sure someone else will post more info...
But if all original, the K will have 4 into 4 pipes, and the F will have 4 into 1 pipes. F series are designated "SuperSport"
Perhaps there is also a slight diference in heads/valves

I don't know the technical details.

I *think*

That the K is more of a "touring" style and the F is more a "sporting" style