Buy the Pertronix for the distributor. Its the shaft that matters. The "d" shaft is the solid one, for the earlier "loadomatic" distributors that have only vacuum advance (no mechanical). The distributors are "non smog". Takes the 1266 or 91266
The "C" shaft is found on the later dual advance (vacuum and mechanical) distributors. It has NOTHING to do with the smog (thermactor), but since they arrived on the scene together, these later distributors are referred to as "thermactor" distributors. Do not confuse dual advance with dual vacuum hookups. Dual vac hooks was a later 70's thing.
Probably someone put a later distributor in your engine -- perhaps due to a carb upgrade to a non-loadomatic carb. Anyhow, you need the 1261 or 91261 Ignitor I or Ignitor II.
I don't know what "problems" folks have had with Ignitor II. It has one VERY useful feature -- overload protection. The Ignitor I will burn up if you leave the switch on, with the engine not running. Both Ignitors need 12v to work properly. Many folks have gotten by with 8v (stock coil voltage, in system with a resistor wire), but its not optimal. If you are going to a FT coil, you need 12v for it too, so I cannot see any reason not to go with the Ignitor II. Got mine from a seller on eBay, clearly someone who was a business, for $90. Not bad, and only about $20 more than the Ignitor I -- cheap price for overload protection.
