Alternator Sizing - Amp requirements

from the builder's test sheet at 2000 rpm shaft speed.
12.8 Volts x 100 amps = 1280 Watts

therefore at 13.5 Volts
1280 W/13.5 V = 94.8 Amps

and at 14.5 Volts
1280 W/14.5 V = 88 Amps

Now there may be a catch in this. It may be that reducing the output voltage also is reducing the voltage to the rotor. That means the rotor is creating a less powerful magnetic field at 12.8 Volts than itwill at 14.5 Volts. In which case regulating to a higher voltage could result in more output power. Without know a little more about the test hookups and the self energizing circuit, we don't know. Or at least I don't know.
I would say that if you derated the 100 amps at 2000 rpm to 88 amps, that would be a worst case scenario.