If they pulsate at a steady rate, especially at idle, in gear, it's your mechanical regulator cycling. The easiest, quickest way to eleminate this is to replace your old mechanical regulator with a Wells electronic unit. VR715 is the number, if I recall. Had the same problem until I swapped over to the Wells unit about 4 years ago. AND, it's only around 10 bucks, and is a direct "plug-in" replacement. Just be sure that the mounting legs are grounded to the radiator support.
MalibuJerry is dead on the money, my '70 Cutlass did the same thing and the Wells regulator solved it for $10 and five minutes of time. They are available at Auto Zone. They don't have points like the OEM ones but are electrically controlled.
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