KAL is a Airline which has not divided CARGO-PAX into two AOC and structures. The Pilots fly one day a cargo plane and the next day a pax ship. They also have code shares with Airlines like LH, AF, LY and others. So the 747-200 F are then used by the partner Airlines. Additional they have permanent wet leased up to several years. That is why you find then B742 in the schedule. Who cares what plane is the freight on as long as it delivered safe and sound. Laptops and Mobile Phones are also transported in PAX planes and then they are in B777 sometimes. The B777F is not delivered yet, so just to answer your next question. Does it make a diffrence?
Fly safe and land Happy
NG