The "2 gauge smaller" rule of thumb is OK, so a 14 Ga. in the alternator charge lead will be just barely sufficient. Personally, I like a little more current capacity. The fuse link is a "last resort" fuse to prevent a wiring harness fire in case of a dead short. It's not some sort of hard and fast rule that will make all your children be born naked if you fudge a little. In today's litigious society, everybody who manufactures anything tries to make their products lawyer-proof and common sense gets tossed out the window. I think a 65-75 amp alternator trying to push its full capacity through a piece of 14 gauge wire occasionally is more likely to cause a problem than using a little common sense and still protecting against a dead short. Your mileage may vary!
Jerry
So 12ga to be on the safe side, 3" long?
