What amp is the alternator?

Oh Shoot. You threw me off when you said you found a pic of a 383 Barracuda. That's a small block in th ephot you found, and I see your engine is as well.
LOL.

Getting a voltage regulator is not a big deal. Whether you want original points type or transistorized version, might take a couple tries because some are bad copies (internally) but they're not rare.

More expensive would be a new wiring harness, especially under dash. Check that out. make sure all the connections and wires are there to begin with. Then deal with condition.