If you were to do this it would be a lot of custum work and relocating stuff there really isn't any room to put in a second alt. Your best bet would be to get a 200 amp or more. If you get bigger than 200 I've read that you'll have to make a custum bracket, and you'll have to move the coolant hose around to get it to fit.
An easy way threw would be to get a good battery and a 200 amp alt. That's what I have. With an e fan and a 2000 watt system and it holds up fine, at night there is a little dimming at idle.