It would be interesting to see how many of the Mustangs were optioned by the buyer, meaning "Retail" order type on the Marti Report.
From a marketing standpoint, most cars had to be built and delivered to the dealers within a price range that was affordable. The price had to be in-line with other cars in this class. I think they call that value?
From a manufacturing stand point, Ford generally had to build cars based on available components and buyer preferences.
A typical 1967 Mustang was a standard coupe, with C code 289-2V, C4 transmission, power steering, and AM radio. Random color mix determined above.