Alt advice

All you need to do is use a dual field alternator with a small external voltage regulator. Any alternator shop can put one together for you for reasonably cheap. The regulator I had was the size of a book of matches and attached right to my alternator. ( if you look closely, you can see it on the side of the alternator in this picture) I left all the factory regulator stuff right where it was and even left it hooked up. I did add a new cable with fusable link from the alternator to the starter relay.

If you add a larger cable from the alternator to the starter relay(use some fuseable link on the end), it will help keep excessive amperage out of your bulkhead fitting and amp guage and route it directly to the starter relay and battery.

This was the only mod I did on my '68 Barracuda when I had the slant six and it worked great. Lights were brighter especially at idle, battery charged way better and ignition worked better. Cost me under $100 for the new alternator, the mini electronic regulator and the cable etc.

PS: I did not have any additional amperage being drawn inside the car. If you have a big stereo or something, be sure to add it at the starter relay and not inside the car, as it would have to go through the bulkhead connections and that's not good. They are wimpy enough to begin with.