There's no need to upgrade your alternator with those amps; there's an easier alternative which is to use a Stiffening Capacitor. The Stiffening Cap' stores energy to help push your amps, mainly your subwoofer amp whenever the music 'hits hard.' You can use a .5 farad (For systems up to 500watts) or even a 1 farad (1000 watts) and you'll be fine. You can find them on ebay at very competitive prices.
check the fuse size on the amps, thats the only way to determine the max power that they use. keep in mind that if it uses 60 amps, that will only be on BIG bass hits, with the system turned up all of the way. adding a 1 farad cap is probably all you need to do.