Yes, use both those lines. Those lines are there to help get the engine and the mounts in the correct position. The 4* already has thrust built into the airframe so you do not have to figuer that out for yourself. You will actually make a cross with the lines and you put the engine right in the middle of the lines. Let me just say though that the plane is such a forgiving plane you can be off a bit and it will still fly nice.