You probably have this figured out already. I installed one on my 78 forever ago, so I don’t remember much. However here is my take on the instructions. 

The point cam has two lobes (high spots) that open the points. The Dyna magnet ring thing has two set screws. I’m gonna guess they are something like 45 degrees apart. So, looking at the back end of the point cam, and looking thru the center bore, one of the two point cam high points (lobe) aligns with the flat side of “D” shaped hole at the end (front) of the center bore. That’s the lobe Dyna is using to register the position of the magnet ring thing. So, slip the ring on the cam per the instructions, and position so the two set screws equally “straddle” the cam lobe identified. Tighten in place per the instructions.