What is the point of this? Will the vehicle keep running if 1 dies? Are the for drivers running a bunch of electronic stuff?
ONe usually runs an inverter like a welder on a working truck.
I work for the largest alternator manufacturer in the world, I see literally thousands made daily and know almost everything about them and nothing else about cars. If you are looking to hook up a badass stereo or giant light bars or something along those lines then that's the only reason really...it will actually decrease power to the vehicle due to DRAG..a single high output aftermarket alternator most of the time will do better than stock duals..kind of pointless imo unless you have the most balling stereo/electronic set up ever in your truck 
Thanks!