I've got a little bit of reference material on some of those distributors by the part number on the breaker plate. Another difference I forgot to mention was a change in point gap and possibly the cam lobe profile in the mid 1950's which changed the "dwell" setting.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!