With standard Tri-Y headers as Doug Thorley used to build them, on one side of the engine the front and rear tubes come together in a Y and the two center ones do the same; on the other side, the front and third come together and the second and fourth. Those combos dump into the collector Y. That is for engines with a 1-8-4-3-6-5-7-2 firing order. That combo of pairing is what this looks like to me.