I also changed mine, I put in a 140 amp Powermaster, not that I think I'll need 140 amps but I don't want dim lights when I have the rad fans on at night at an idle.
I went with the three wire as you can still have the idiot light ,as well as a volt meter, and the alternator senses the voltage in the harness not just at the battery. You could have a voltage drop and have less voltage in the harness than at the battery and using the three wire the alternator will sense the drop and charge to that.
My car is a 68 yours may be different. The regulator has four wires at terminals 1-4 in a large clip. The orange one comes from the fusible link and is connected to the main splice in the wiring harness by the horn relay. It connects to number three terminal. Number four terminal has a brown wire which is powered from the ignition switch. The number one is blue and the number two is black and white, they both go tho the alternator. I spliced the orange wire from number three to the blue wire that went to number one, and I spliced the brown ,ignition switched wire from number four to the black and white wire that went to number two terminal. The blue wire then goes to the sense terminal of the new alternator and the black and white wire goes to the other terminal. The heavy red output wire from the old alternator attaches to the same output post on the new one.
Or forget all the splicing and connect the sense terminal of the alternator to fusible link at the main buss and the switch terminal to the brown wire that comes from the firewall block to the old regulator.
Now that I have my engine out again I will re wire the whole engine compartment and eliminate the splices at the horn relay. The voltage sensing wire will come from the firewall and the switched wire will come from the firewall connection block.
It is an easy switch-over and I hope I didn't muddle it up and make it sound to more complicated than it really is.
Please check and make sure your car is wired the same as mine before you splice any wires together.
