Bob,
here you'll find the wiring diagram of different 911's:
https://classickabelboomcompany.com/wiring-diagram-porsche/
If you want to stay with the stock SC distributor then you have to stay on an ignition box capable to handle with inductive pickup. Porsche introduced CDI on the 911 in 1968
afaik to make them more reliable. But in the beginning the ignition was triggered like with normal breaker setup. These were the 3pin boxes. Inductive pickup came with the SCs and 6pin boxes. Either you change the 1970ies wiring harness to use the 6pin CDI box or you change the whole ignition.
In general the engine itself can be managed with breaker or inductive pickup, this makes no difference. It's more a matter of your personal choice and what you want to achieve. Is the SC dizzy in good condition, does it still advances and retards as it should? Did you checked it yet?
The 3pin CDI box won't work with the SC dizzy because the 3pin boxes are managed as a breaker ignition as said. SCs started to have inductive pickup from the beginning. You can replace the 6pin CDI box to e.g. a MSD6 or Permatune box or similar. But the SC dizzy is always inductive pickup. The MSD6 can operate either with inductive or breaker setup.
I personally use an 123ignition tune USB version dizzy with a Permatune box. My 123ignition dizzy is the older version with a breaker setup intended to be used on 911's up to 1977. I use it with a Permatune 3rd gen GS (=general service) box which is basically a breaker triggered CDI box being used in many other vehicles too.
You can waive the CDI box when using a 123ignition and connect the tachometer to it's output and 123 coil, but then you have to protect the tachometer, beause the bursts coming from the coil will damage it for sure (you connect both on output of the dizzy). The spark of the combo 123 with a fitting coil might be as strong as them from a CDI by todays standards (IGBT FET transistors simply switch faster/quicker than older simpler tranisstorized ignitions).
My choice was to stay with CDI paired with a modern and programmable ignition curve beause of some changes on my engine, see my footer. Pretty happy with that.
Thomas