The really large diameter alternator pulleys were designed for use on engines that would see continuous high RPM use, and they significantly reduce alternator output at lower engine speeds.
In my opinion, I would not use such a large alternator pulley on a car that sees regular street duty. Maybe the handful of horsepower gained would be worthwhile for a serious track car, but there are too many disadvantages for a street car, even if you don't have a big stereo or other big loads. Your 60A alternator only makes that much current when it's spinning around 5000 rpm. (Engine RPM approx 2000) When your car is idling, or anytime you're driving slowly, the output is less. The output is also less when it gets hot.
Now think about the current your car needs to drive on the street, and remember, anytime the car is running, the alternator is the primary source of electrical power. Here are some ballpark current values for typical systems, which your particular car may or may not have.
1 - Ignition 5-7 amps
2 - Fuel pump 7 -15 amps or more
3 - Headlights 9-12 amps (low beams)
4 - Electric radiator fan(s) 20-45 amps
5 - Heater/AC blower fan 4-10 amps
6 - Radio 2-4 amps
7 - Wipers 8-12 amps
8 - Turn signals 2 amps
9 - Brake lights 2 amps
10 - Other? (Stereo, additional lighting, computer, dashlight bulbs, dome lights, horn, etc)
If you start adding things up, you can see it's not hard to use up 50 amps just driving the car normally, which only leaves 10 amps (under ideal conditions) to re-charge the battery.
Add in a moderate car stereo amp, and a set of driving lights, and your alternator could already be too small. This is why I don't suggest a 5" alternator pulley on a street car. You'd need to keep the engine rpm's over 3500 for the majority of the time, just to keep the battery charged.
