Differences between earlier /6 engines and newer ones

The crank spacer ring is not a standard part, but custom-fabb'ed by some nice people with lathes. I got one from member Charllie_S here for ~$20, or if he is dry try TorqueFlitePatty (or such) who I recall is also on ebay. BTW, I understand it is the same size as the spacer ring needed for small-block engines too, at around the same time, so if you run across that it "should work". I never heard that Chrysler dealers sold one.