yes you are correct about the time line and original equipment would not have been PP type
original top candidate types are (wax)paper-foil or metalized paper types

upon looking into who still makes metalized-paper types i see there are common for audio and some high voltage applications (but in a oil bath types), both Kemet and Cornell Dubilier have a line of metalized-paper, but not in the appropriate styles for automotive use.
but that doesn't mean they are not still made for legacy support and simplicity and just not easily source-able directly to us, we would need to dig deeper into who is actually making the automotive ones today.
I believe the top two candidates for the modern capacitors may be metalized-paper still or new PP type.


some history that probably has mistakes:
PP capacitors were only just invented in the early 50s (in the lab) and likely didn't start showing up on the market until the late 50s or into the 60s.
before that, the distributor capacitor was likely either wax paper-foil or metalized-paper type.
the other technologies for capacitors at that time were not suitable
mica and ceramics - not easy to be able to get the large values you would want for the distributor capacitor, over kill for that application and would be too expensive, good for 0.01uF or smaller values
PET types were first introduced in the 1940 but would not have replaced a robust well made paper-foil or metalized paper type capacitor yet, it was too expensive and not well known for reliability at elevated temperature.
Aluminum electrolytic - not suitable too much internal resistance for pulse applications, too delicate and failure rate too high for operation under the hood of a vehicle. They were first developed much earlier than PET and PP types at about the turn the the 1900 in the laboratory and slowly came to market in specialized applications all the way into the 1930s, but they were notorious for being low quality and failing easily. It wasn't until military demands in WWII for better quality aluminum electrolytics drove new innovation to make them generally usable.
So starting just after WWII aluminum electrolytics became a normal component in electronics, then newer different types of electrolytics were gradually developed now that the market for them was established.

I'll see if i can track down who is making the exact suppression caps we use today
-s