This spacer, or distance piece, has 2 different numbers in the parts books, one is for all models, and one is for "AC" ign. When used with corresponding sprocket and rotor, and without key, different timing positions were used via 3 holes in rotor. That's what this is. The one you normally find is smaller diameter but same thickness. I wouldn't dare leave it out, I'm not sure the rotor would tighten up, or if it would cause primary chain interference. I wonder if the ET setup, used with conventional stator, would secure rotor when keyway is damaged? Just thinkin.... As far as racers losing the alternator, they used a long spacer ( the center knocked out of a rotor works well), or cut the end off the crank, drilled and threaded for a bolt. Some race primary covers won't fit till this is done. My .02.