The top cover clamps down on the bearings and holds them (and the cam). At first glance, this looks wrong because the inner bearing hangs off the casting a little, but its the way it has to be. The bearings need to pushed in as far as they'll go on the cam so it can't "float" left and right while spinning, throwing the sprocket alignment off. The bearings must be inset into the head to allow the points and advance housings to seat fully and seal. The housings have a step on the back that sits into the bearing inset .....