How much amperage can an alternator support? no really...

[Vittorio Bares]

I've got 580 watts of lights on the rally car, this will require 48amps
to run. Typically the 4000 has a 90amp alternator, I know I could go
with the heftier 110amp alt from a 200 or what not. 
 
But my question really is, how much amperage does the car need to run?
The only other acc I have is the heater fan, radiator fan, a few gauges
and lighting for those, brake lights, fuel pump, intercom system -
potentially the wipers. How much amperage does an alternator (typically
20 years old) really produce?
 
My assumption is that the big current draw is going to come from the
radiator fan, fuel pump and possibly the heater blower fan - but also
the ignition (spark, etc)...
 
Thanks,
 
Vittorio -