Charging issue 68 barracuda

Did you replace the alternator?
If so, take a photo of the back. One brush should connect to the green wire (feed from voltage regulator). The second brush should be grounded. If they sold you a later style alternator, you'll have to add a ground wire.

Your mechanical regulator (in the photo from 2017) it looks like the fusible links are blown. Yes?
If so, need to figure out why.
That may or may not be related to the current problem.