I have a multimeter that works, but I know nothing about electronics to be honest with you. Do I set it to AC or DC to test the alternator? If I guess and I'm wrong I have heard multimeters can bust. So it looks like the 65 watt is the winner.

 

An alternater will only produce as many amps as is needed. Your stock alternater is capable of producing 42A, at max you're probably only drawing 40A. If you install a 130A alternater, it will only produce 40A, because that's all that's needed. Going for a bigger one just adds cost and weight, and increases parasitic loss.

If you want an exact reproduction of the original part, got to one of the mustang parts suppliers and pay the big bux. Or, get a rebuild kit and rebuild yours.

If you want one that works, go to Autozone (or wherever) and get a stock replacement. Get one with a life time warrenty. They're inexpensive, and you'll never have to buy another one.

The original voltage regulaters were mechanical, and they do wear out. Replace it with an electronic one that will last almost forever. Again, get one with a lifetime warrenty.