However, other retro fits are different. I know of at least 3 types of FMC fitted to Classic 747s, there may be more. And I've used 4 diffrerent makes of FMC and they're all different.
Perhaps if you mentioned whose 747-200 you are going to fly, you may get a more helpful response. Oherwise you could waste your time learning an FMC not fitted to your aircraft.