Not to keep beating a dead horse, but in the link provided by Neptune on the Transformers Saleen S281, the Saleen website does indeed use the word “Mustang”.
http://www.imcdb.org/vehicle_128980-Saleen-S281-2007.html
http://www.saleen.com/transformers.htm
As does the dealer locator portion of the Saleen site: http://www.saleen.com/dealerLocator/DealerLocator.aspx

I would be curious to find out how the cars are registered, maybe from someone who owns one. N.A.D.A. (National Automobile Dealers Association) also lists them as “Saleen Mustang”
http://www.nadaguides.com/default.aspx?LI=1-22-1-5006-0-0-0&l=1&w=22&p=1&f=5012&m=1348&c=13&z=63010&da=-1&y=2006&da-1
eBay lists them as “Ford Mustang Saleen” and when you decode the Vehicle Identification Numbers (VIN) provided on the eBay listings, the results identify the vehicle as a Ford Mustang...
https://www.fleet.ford.com/maintenance/vin_tools/default.asp So unless Saleen generates a new VIN, I don’t think the Mustang basis can be ignored.

Further, some still have the Mustang grille emblems in place. I am of the opinion it would be best to list these with “Saleen” as the make and “Mustang” as a portion of the model name. I believe that if “Mustang” were somewhere in the name, it would go a long way towards preventing confusion and minimizing arguments.