Dual alternator coupler bars (2) for GM V-8 and V-6 engines with this drivers side air conditioner mount serpentine belt.  Fits most 1996 to present. V-8 and V6  engines. COUPLER BAR PLATES ONLY -  (the black part joining the two alternators at the top  the front and back ) you will need to source the idler pulley and other parts - a bone yard will do fine for the pulley and spare alternator often.  A CS-144 alternator will also fit with the same mounting holes.   GM wiring schematic diagram  and parts list is included - including recommended belt size. 

This is considered a custom order item and is not returnable.  Custom Made Item Not Refundable or Returnable

GM never made a factory dual alternator option fo the gas engine as far as is known, this is an aftermarket solution

You need dual alternators if you have a high amp stereo or  to run any decent sized Hydrogen Generator system and the pump required to feed it at idle as a single alternator will not put out enough amps - even a high amp one