The problem with upgrading the Hitachi alternator in your Isuzu, is the fact that while you can upgrade the output with a rewound stator, no one makes a heavy duty version of the bridge rectifier. The extra power generated by the upgraded stator will easily burn through this weaker bridge rectifier.
We do, however, have an external second bridge rectifier. This allows you to have an upgraded, high amperage alternator with a durable double, or even triple set of bridge rectifiers. The links below will direct you to the alternator you need, and some information about the Quicktifier. You can also call directly at 1-616-785-7990.
http://www.alternatorparts.com/nissan_pathfinder_w_quicktifier.htmhttp://www.alternatorparts.com/Dual_Remote%20Rectifier%20System.htm