Honda-SOHC

Hi, i have a 1976 cb750f that i am rebuilding. I had to buy carbs that i rebulit and the airbox. The problem is i don't know where the hoses go to and from the airbox. one has to come from the valve cover and one comes from the top of the airbox, but there is a breather valve under the battery with three ports and i do not know what goes to what because i am trying to get the best performance out of this oldy but goody.

thanks
Erin