Distributer case is "earth". A wire is only needed if the dizzy is very loose in the block or some fool put an "O" ring on it. The clip to earth wire is for peace of mind. Better solution is the ground(earth) strap from the bell housing to the frame. To set your mind at ease, put an Ohm meter on the block to the mount screw on the points. 0.0 Ohms? Good to go.
