Ported vacuum doesn't come from the throat where the airbox is, it comes from the other end, where the throttle blades are.

All the vacuum lines can go to one place.

I suggest going down to the library and ordering the weber carburetor book, it will show how to do the vacuum. This one I looked at is Haynes. It even listed jetting for a few Datsun models. Here's another i haven't seen yet: Weber Carburetors by Pat Braden