I just spent this past weekend with this bird. It is N51DL 44-13257, the Cavalier prototype Mustang. It has been in a brown/green camo scheme for about 12 years, and is based at Sarasota, FL. Ed Lindsay, son of Cavalier founder David Lindsay, flies it regularly.
Not sure if you're interested but the first photo looks like it was taken at Fox 51 at Denton,TX.