I suspect that your model has been repainted. Which would ofcourse take a CONSIDERABLE amount of worth off of it. Nevertheless, if it is verifiably Grumman in origin, you have a gem. How sure are you that it is Grumman manufacture? I suspect that based upon the rather crude shaping (paint aside), that this was a novelty intended for the masses and not a Grumman model used for any engineering or marketing purposes. But I have been proven wrong on more occasions than Lanc has copulated with sheep.