if you are going with a Braided fuel line it should be AN-8 all the way, if you are going the Alum way, 1/2 all the way too, in my opinion go w Braided fuel line, is pricier than alum but it's about your security and piece of mind.
I have this set up: AN-8 from the tank to regulator, the reg has 1inlet and 2 outlets, please dont put the cheapy "Y" line to your carb, instead run the AN-8 fuel line from each of the outlets of your regulator to each of your carb bowls, that should do the trick.