Alternator?

According to the dealer sales book, '50 amp' was standard with A/C, and '65 amp' was standard with electric window defroster grid.
p. 16
The 1970 Hamtramck Registry - 1974 Plymouth Dealership Data Book - Valiant/Duster
If it came with rear defrost and 65 amp alternator, it would also have been equiped with the matching wire harness. So these things would be pretty obvious. A guy posted some photos of a rear window defroster and harness from a '73 within the past year.