You're actually setting 2 separate ignitions here, one for each cylinder. Adjust the top points set (right cylinder) 1st. Loosen the 2 large screws (red arrows) and rotate the whole backing plate to do this. Next, move the test light to the bottom points set (left cylinder), check and adjust it's timing if need be. To do that without disturbing the top set's adjustment, loosen the 2 smaller screws (blue arrows) and move the half plate the lower points mount to. If you move the whole backing plate again, you'll throw the top set off .....
This pic is missing the lower points set because it is of the single points set-up I used to run. The half plate for the 2nd points set is still there because it holds the felt lube pads.
This pic is missing the lower points set because it is of the single points set-up I used to run. The half plate for the 2nd points set is still there because it holds the felt lube pads.