Blowing voltage regulators

Old Mopar alternators don't charge much, or any at all at idle speeds. Even more if parts are changed overtime, wiring is getting old and maybe a larger pulley is mounted on the alternator, limiting it's charging rpm even more.
If originality is something you care about, you could decide to upgrade to a dual field alternator and regulator. They look similar to the older ones and they work a little better than the single field alternators.

If you just want to fix it quickly, get a '90s Nippondenso alternator out of a Mitsubishi or something like that.
They have a built-in regulator and only have 2, maybe 3 wires, and will charge at idle and provide a steady 14v charge at all times.