In a situation like this, where a model is special (rarity, passing of a generation, etc.), you risk a lower trade in value than if you just were trading a plain vanilla car. By all accounts you have a great example and HD pack would add to it's uniqueness but it should bring good money even without it. I would run by the dealer or Carmax to get a base line trade in value / buy bid. Then you can list it on one of the national platforms and see what bites you get at a higher value. You will undoubtedly get well-above trade in value, it should more than cover the lost tax savings. The other option is to put a listing on a couple of enthusiast forums like this one and see what interest you get, should sell very quickly.