I'd say you want a -4 line from the front (rear in car) sidehousing (Mazda knew what was right so use the port that is already there) to the higher port (not the overflow) on the filler/expansion tank.  Us a -6 or so line from bottom port on exp. tank to the pump outlet or highest point in cooling system.  If the tank is the only filler point it is kind of a pain to fill the system but after that it's no problem.  Keep tank 1/2 full when cold.