The tall cap distributor got introduced with the 12 volt ignition system, mid-1955 model year. The higher firing voltage available with 12 volts (14.7 with the charging system running against a fully charged battery) made it more likely for the short cap distributor to "flash over" to the distributor housing if a plug wire came loose. The tall cap and rotor don't fit the "short cap" distributor properly, as there's a slightly different height shaft above the point cam.
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!