How many using an A500 overdrive ?

There are some differences. However you can swap the entire lockup trans and converter into a "A' body with a 1968 or newer slant six or small block. 1967 and older engines had the small converter hole in the crank, and the later converter/trans will not fit. The early lock up trans was controlled internally by hydraulic pressure only. The later ones (not sure what year) the lockup was controlled with hydraulic pressure controlled by a electrical solenoid inside the trans. If using the electrical controlled trans (has a extra electrical connector at the rear of the main case, near the tail housing) you need to supply 12 volts (I don't think it is 5 volts) to this terminal when wanting to lock up.