I will agree to an extent, Fords initial planning was to sell as many V8 Mustangs as possible, but as the rate of sales were picking up, many decided to just opt for the standard I6. I have had many ask me if the V8 only came with the GT and the fastbacks, but this is completly false. If you really think about it, why do you suppose there are less production numbers on fastback today? And why are they becoming so hard to find? Well believe it or not, back when the fastback was introduced in 1965, mant critisized its looks as "too bold" and many didnt like them.To show a point, production numbers werent very good for the Fastback. For the people whom did, a lot didnt have money but just wanted the "look" of the classic, and just got the bone stock essentials. There used to be a time where you could see fastbacks everywhere and many didnt want the 6 bangers, so the hoods were slammed. But with the increase popularity of Gone In Sixty Seconds, and Shelby making production cars out of Fastbacks, where does it end? Fastbacks are coming up far and few between these days, my suggestion is if you got one, keep it!

Im unsure what your asking me with the assembly plants, are you asking if Ford knows where the millionth Mustang produced is at?