64 65 used a ball and trunion drive shaft.they also used the speedo gear thats one piece and clips on the cable.My 65s still works great.66 up 4 speed you change speedo gear and cable along with slip yoke drive shaft.Disc conversion find a 73 up A body or Diplomat,Aspen etc,They have taller spindles but seem to work better.You should have the old style rear also.Axles need changed.65 to 70 B body is a direct swap or Dr Diff has a conversion kit.If its was a /6 car you need V8 K member or the conversion mounts.Rocky