Unfortunately, it's very difficult to sell a modified car over the "blue book" value, even if the modifications are well done and desired by the buyer. A lot of this has to do with the fact you've restricted the pool of people willing to buy the car in two large ways. Combine these with the sluggish economy and you might have an uphill road.
1. They want the same modifications you've performed on the car.
2. They have enough cash in hand to cover the difference between the "blue book" value and the asking price, because no bank will finance more than the "blue book" value.
Good luck with the sale.
Duncan