I'll ask the question of what are you trying to fix?
Fine if you have problems like 68 Firebird400 had. But those are the exceptions. Lots of cars still run the original system (100% did for years, since there weren't other options). The regulator has temperature compensation built into it (required for proper battery charging) so you have already have a key feature.
The larger output alternator - again why? If the electrical loads have increased (i.e. you have added electric cooling fans), then that may be required. But the original output of the alternator exceeded the electrical requirements of the car. There weren't many loads in a late 60's car (radio, lights, ignition).
If you do get a higher output alternator, be aware that the # that is quoted is not relevant to normal driving. You need more power at idle (esp for cooling fans). Ask what is the output at {your idle engine rpm times the pulley ratio} (often about 1800 alt rpms, but calculate yours).
