First up, ditch the 42 amp alternator. The extra load of audio gear on the charging system will actually kill engine performance (I have seen guys running big amps with a stock charging system and heard the alternator belt screaming from being under load ). I'd be going large - try and source something like an 85 amp alternator. Get a decent battery to back it up while you're at it. A strong charging system is your best friend and often gets overlooked when thinking about performing mods.