The 50 was an approx number since the company did not want to share the full number. We do know that the front ends were unpopular (peope did not like the design, too expensive and it was not a simple "bolt on) Since we know they measured success when they sold 100-200 plus of a kit its a fairly easy guess.
Currently I know of 14 original front ends. In recent years a couple of owners have made molds from their front ends and sold them to others. Some of the details are different on the reproductions I've seen.
FIberFab sold two different versions of the Mustang ET front ends. A convensional front end that was a single pice that included the nose and both fenders. Hood was separate and was installed like the normal Mustang hood. The Competition front end was a three piece item with two small panels that were installed behind the front tires and a large tilt front end for the rest. There are more of the conventional front ends around today .... my current one (owned two over the years) is the Comp. model
Through the years a few have been installe on race cars and one was even used (and destroyed) for a B movie "Joy-Ride to Nowhere"
Jeff Speegle
MCA Shelby Gold Card
http://www.geocities.com/MotorCity/6473
Mustang & Shelby research, documentation
http://albums.photopoint.com/j/View?u=1609818&a=12284202&p=44925357&Sequence=7&res=high.jpg