You're talking the metal terminals?
It depends on which connector your replacing.
AFAIK Chrysler used SAE 12 ga for the alternator output, although it some point IIRC it wsa bumped to 10 ga for standand option,
Most everything else was SAE 14, 16 and 18 gage. No 20 gage in the 60s.
However, the commercial F crimp terminal sizing seems to be based on typical AWG sizes and insulation. So in my experience its good to have a few options in case it seems like The crimp is loose.
This will give you an idea of what's out there for us.
Sources for Chrysler type wire terminals