The name/term "Mustang" is used loosely on these cars (almost like a nickname) as they have very little, if any Ford parts. They only look like a Mustang, just as a RUF looks like a Porsche.
http://www.ruf-automobile.de/content.php?seite=&rubrik=&id=&lang=en

See this clip – note what the narrator says later on in the clip about the car…
http://www.edmunds.com/insideline/do/Features/articleId=121424

And here – The car does not have any Ford emblems…
http://www.edmunds.com/insideline/do/MediaNav/articleId=121424/firstNav=Gallery/- photoId=41635

Recently, Saleen has been given recognition as being it's own full fledged car company – not a tuner company. Because of this, Saleen is subject to the exact same federal regulations as Ford, GM and so on. Saleen numbers each car individually before it’s release for sale.