I haven't assembled that plane for anyone but the hole is usually just for your fuel lines. The horizontal and vertical line is where the crank should line up to. Some of the planes have the fire wall already set at an angle for the engine thrust so they off set the vertical so the engine lines up to the center of the cowl. You can just measure to find out if I'm correct, I'm pretty sure this is what it is about. ARF instructions are a bit light on things like this but you probably will have a couple of degrees of right thrust on the engine.