The stock alternator is more than adequate unless you are pushing some serious wattage with your stereo or have other power robbing accessories.

If your alternator is working there is no need for the upgrade. However, this is a perfect upgrade if your alternator needs replacement.

 

I'm not sure about clearance but perhaps you could try an alternator out of a 13b or 20b Cosmo?

The 13b had a 90amp or 100amp alternator from memory, and the 20b has a 120amp.