It would be wise to use all the electrics that come with the alt you choose, an alt produces AC not DC, so 1st the wave is chopped by a circiut to produce a DC like output then it must be regulated in terms of its charging the batt.
My advice would be get the entire system from a scrap vehicle so it all matches. Some alt have the electric bits in the back of the alt but some did not. Choose a vehicle with a large capacity or 1 to match your vehicle, fiat 500 will not do. guess it may be best to also select aa vehicle with similar rev range, so lotus is also out.