I will have to check my Delco books but I am pretty sure the cam lobe assembly itself changed and with a new cam lobe assembly, for example the 2403 distributors, came a change in dwell time. That occurred coincidentally around the same time the switch from 6 volt to 12 volt occurred. That being said, my Delco books list the 2403 distributor as the service replacement for the earlier distributors which is another reason that leads me to believe there was a difference in the lobes. I will check though in my 59 GM catalog when I get home tonight.
