Ed Whitney puts together both a 6V and 12V alternator that looks like the OEM generator. See the following Fordbarn thread:
http://www.fordbarn.com/forum/showthread.php?p=66672
I'm not sure about the ability to mount a fan on it, but a call to Ed will answer that question. I've had his alternator on the truck for over 5 years with no problems whatsoever.