Here is all you need to know to set the fuel level in a fuel bowl for 240z from 1970 to 1971 inclusive (You will have to deal with the oddball bowl in the 72's however the FSM states that the fuel level will be the same in each bowl). Below are two marks at 20mm & 23mm down from the top lip of the fuel bowl.  The FSM shows the fuel to be 23mm down from the roof of the fuel bowl(which is 20mm down from the top lip  but it may be a typo. Pick one and be happy.     The