Ryan,
The voltage regulator supplies current to the field windings of the alternator. Increasing the current increases the output voltage. Since the regulator is fried, it likely is supplying max current to the field windings, and therefor is tripping that breaker. (also the high output voltage is a good indication of max field current. I am betting that water (could have been rain) entered the system at some point and took out the regulator. I know that $350 is a lot to part with, but I would recommend replacing the regulator rather than try to find an individual part. Once a board has been stressed, other failures are likely.
This is a spec sheet on your genset...
http://www.cumminsonan.com/www/pdf/s...ets/a-1351.pdf