And although the Dish 300 - 18" dish pan, should work if the LNBF has a DP (or DishPro) on it; the Dish 500 has a larger dish pan and should provide a better signal.
Depending on your location a D300 will be fine but if you can get a D500 with an I bracket that's better. And if you can get a 24'' dish, even better. You get the picture, with 129 size DOES count.