Chuck,
The leading edge faces the direction in which the piston travels when depressing the clutch pedal. Did your rebuild kit not come with an illustration? I've seen a number of off branded kits lately with no instructions, which I think is cheesy, but I'm afraid is the wave of the future...
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon