You only need the 2 pice for a full delete. I went ahead and got the 3 piece because I think it looks cleaner by filling in a little bit more of that space back behind the pony. Some people say it doesn't make much difference but I think it's a little better than just the 2 piece. But yes, the 2 piece is all you really need.
The pony connects by 2 screws that go into 2 existing holes in front of your radiator and a tab at the bottom.
I also went ahead and got a Roush bracket that keeps the corall around the pony, trying to keep as much chrome as possible.