Referring back to custom's pics: The reason for the different heights is the shorter adapter is for a Autolite and the taller is for a Delco distributor. If you use a Delco adapter adapter on an Autolite, the bottom tabs on the Autolite will not contact the intermediate shaft. So the motor turns over, but the distributor doesn't turn.
As a reminder, the tabs on the bottom of the distributor are offset so you can't put the distributor 180 out of time - IF the intermediate shaft is not disturbed. The intermediate shaft can be installed 180 degrees out. And the distributor turns CCW instead of CW like most every other engine you will encounter.