Why bother messing around? If you're a new customer with D* just go with a new Dish, recommend the phase III. Why not when you can get a 35 hour DirecTivo installed with the phase III dish for $59.95 http://www.valueelectronics.com/Hughes_tivo.htm which is only $20 more then the regular 18 inch dish.
This turned out to be super easy. I bought a Phase III oval dish, built it with the correct tilt angle, and hauled it up to the existing mount. Five minutes of attaching cabling to the LNB and six minutes of alignment, and voila! DirecTV. It helps that my azimuth for the new dish was within 4° of the old azimuth.