How do you adjust the interrupter commutator switch rod on a 1970 Chevy Nova?

The upper section of the shaft has secured there to an arm, which is adapted for rotation with said shaft, the said arm having pivoted upon its outer end as indicated at one end of a lever. The opposite end of this lever has pivoted there to as shown at an interrupter arm, the said arm being pivoted intermediate its ends, and one end of which is provided with a contact point, which is adapted for engagement with the contact point, which is adjust-ably mounted upon the lever by means of a bracket and an adjusting screw.