Squareback vs round back alternator?

Mattax said
I think that ballast resistor will work OK. make sure it measures what they claim.
From the 1960 Dodge shop manual
View attachment 1715890461

1965 Plymouth Shop manual
View attachment 1715890462

So .5 to .6 Ohms is probably correct match.

The older orignal ballast resistors are made with a metal bracket for mounting. Othewise the shape is same.

As for the ballast resistor I cross checked your number #2095501 and the one I have in the Valiant book #1889545 and it turns out they have both the same values. Except in my book the resistance isn't shown.
IMG_20220317_170851 (1).jpg