Phil,
Were there any other options on this particular Mustang, A/C, AM/FM, etc? From what as been determined, Ford scheduled cars for easy shipment and a Dearborn build, San Jose DSO would not be standard - but if a certain option was ordered, and Dearborn was building Mustangs with that option, it would be made there. Also, consider this - San Jose was behind schedule, and Dearborn could help out.
Jim