IIRC, the standard V8 alternator output was only rated at 37 amps. I plan on getting a rebuilt unit that was made for a late 60s full-sized car. I'm told they're rated at 65 amps and look the same as 65-66 Mustang alternators.
There is a vendor on Ebay who regularly sell an 100amp Alt. the price varies from about $60 to $85. He has very good feedback. I purchased one but have yet to install it. It is in an identical ford case, you basically can not tell the difference by looks.
You can also have yours rebuilt to a 95 amp ouput. A reputable alternator shop can do this and the rebuild kit is available.
1966 Red Conv (200)
1966 White Pony Int.(289)A Code
1966 Coupe (289) C Code
Jegs Performance sells the chrome 1 wire variety. Price was about $130 when I ordered mine. They sell a one wire just for Fords ---- that's the ticket. The one wire removes a lot of electrical problems in 40 year old cars (we are almost there).