http://www.4alterstart.com/

the alternators here should be perfectly fine for you
i found a 150 amp for mine for about 250 bucks or so
check how many fuses your amp has, add the amperage together and that'll be your MAXIMUM current draw, which happens extremely rarely and probably won't anyway unless you're doing SPL competitions. at the most you'll be drawing 75% of that amperage on average.
so you can subtract that amperage from your HO alternator, and if there are more amps left over or equal to the output of your stock alternator, you can run that shit as long as you want without the rest of your electrical system missing a beat.