All a 100 amp alternator will do is put a heavy load on the engine immediately after startup when it's replenishing the momentary heavy current draw on the battery by the starter. 65-75 amps is more than twice the capacity of the generator you're replacing. Anything more is foolish unless you plan to run heavy current draw accessories like a gazillion-watt sound system or huge off-road floodlights, etc.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!