Generally the hardest part of a dual alt setup is finding room for it, making the brackets, and getting the belt right. Another option you have is checking with your local alternator shop to find out how much a respin would cost. Usually less output than a true H.O. unit, but also less money (if available for your vehicle). Its a good in-between choice.
I have an amprobe that will tell the amount of current passing thru a wire when placed between the leads. I got it from my old man. Its made for 120 volt I think, I haven't played with it yet. I need to find out if it will work on lower voltage.