I looked at my 1973 PET and found in Main Group 1 105 Air Cooling
the following illustration:
Note item 8, the woodruff key.
Looking in main Group 9 901: alternator distributor, I found the following Illustration:
Note the Items on the second row. After the rear facing housing, you see a spacer, woodruff key, spacer and a nut. It appears these items are behind the blower fan.