First, whoever told you to replace the ballast resistor is wrong, that is a part of the ignition system, not the charging system
Second, is it possible to post some pictures of the voltage regulator and the alternator? Chrysler made some running changes during the early 70's, some parts have to be modified to work in the older cars,
Third, Do you know if the new voltage regulator has electronic internals, or mechanical? It is possible if it has the mechanical internals for the regulator not to be calibrated correctly.
Fourth, It is also possible your ammeter gauge is going bad, all the voltage used in the car is fed thru the ammeter. With a volt meter hooked across the battery and the engine running you should have a steady 14.2 volts.
Good luck and welcome to the site. Bill