What alternator should I buy?

Cant just put on an 80-amp alternator without doing the ammeter conversion or bypass or your gonna have issues. I believe the stock one is 60-amps? The wires are most likely to small to handle the current safely so you need to change the way the wires are routed and the size of the wire from the alt to the battery. I know more about the pre 70's electrical systems but I think they are similar. There are several threads on the alternator upgrade on this site and that would not be a bad upgrade.

However, the complaint is about dim lights and this issue is easily resolved by changing the way power gets to the lights via the conversion I mentioned above.

Good luck.