Fusible link ????

6" fusible link is pretty standard.
I'd consider 12 gauge to be minimum spec for a wire carrying charging current. It'll do the job, but if it's being done with new wire, why not upgrade? Cost is one reason. If a serious race car, weight is another.
I use 8 gauge with a 12 gauge fusible link and have people tell me that's too small (it isn't for my applications).