Where the leadouts exit the wing and how close they are is important when you get to a serious stunter (oops, Precision Aerobatics plane) but where they are shown on the plans will suffice for now.

I'm guessing that the product engine you have has a white plastic backplate. Do you remember which plane it came out of? when you mount the engine, look into the slot where the fuel tubing connects to the needle valve and make sure the intake has space to get air. If not, you may need to add washers or a spacer so it can breathe.

George