The best answer to this question is "usually not". Many factors could cause a discrepancy between a scheduled build date and an actual assembly date, such as shortages of parts, worker strikes, and any number of other things. From what we've seen, the actual assembly date tends to differ from the scheduled build date. As an example, we know that the scheduled build date for the start of 1969 model year production at the Dearborn, Metuchen, and San Jose assembly plants was "04G", or July 4, 1968.
A frequently asked question
There's a common misconception that the 5th character in the Vehicle Identification Number (VIN) can be used to determine if a car is equipped with a Cobra Jet (CJ) or Super Cobra Jet (SCJ) engine. The myth is that Q-codes are CJs and R-codes are SCJs. In truth, these codes identify the type of induction system installed during factory assembly. 1969 - 1970 428 CJs and SCJs that were equipped with standard air cleaners are identified by the letter "Q". Ram air induction is identified by the letter "R".
Positive Crankcase Ventilation (PCV) is an automotive emissions systems that's designed to direct combustion chamber gases that enter the crankcase into the intake stream to be re-burned in the combustion chamber. Polyvinyl Chloride (PVC) is a type of plastic polymer that's used to create industrial and consumer products. If you found this page by searching for "PVC" or "PVC valve" you probably meant to be searching for "PCV".
Contrary to most published literature, 428 SCJ engines were originally equipped with cast pistons. Some of the confusion may be because of the later 429 Super Cobra Jet, which was originally equipped with forged pistons. See the CJ vs. SCJ page for details.
Contrary to most published literature, documentation describing the Detroit Locker doesn't appear from Ford until approximately November 1969, which is well into the 1970 model year. Earlier documentation that I've seen, such as original invoices, clearly describes the "W" code differential as a "Traction-Lok" differential. This is an ongoing research area, and it would be very helpful if anyone who might have documentation describing an original Detroit Locker installation in a 1969 Mustang could share their insights.
Starting in 1969 Ford began offering an optional 3.91:1 gear ratio that used Ford's Traction-Lok differential, which used a clutch pack for quiet, streetable rear wheel locking under hard acceleration in a straight line. Order this option and you also got a 428 SCJ engine!
Starting in 1968 Ford began stamping partial VIN information on a pad just under the back of the driver's side cylinder head of all factory-installed 428 Cobra Jet engines to comply with Government-mandated regulations. Partial VIN stamps have also been found on cylinder heads in the area just above this pad. Service blocks didn't receive VIN stampings, so as engine swaps have taken place over time it has become very difficult to keep up with this "matching numbers" reality.
Ford did not install a rev limiter during the 1968 and 1969 model years. In 1970, Ford added an electronic engine RPM limiter/governor to Mustangs equipped with 428 Cobra Jet engines and 4-speed transmissions. These units limited spin up to 5,800 rpm in an attempt to keep warranty claims to a more manageable level. Fortunately (or unfortunately, depending on how you look at it), removal was quite easy and a great many of these units have failed to remain attached to the cars they were originally installed in.
428 Cobra Jets and Super Cobra Jets used the exact same induction systems and cylinder heads. What makes a 428 Super Cobra Jet unique is the specialized reciprocating assembly.
428 Super Cobra Jets were available both with ram air induction (identified with VIN engine code "R") and with a standard air cleaner assembly (identified with VIN engine code "Q"). The engine code isn't what determines installation of a Super Cobra Jet engine; it's the rear end codes of "V" (3.91:1 Ford traction-lok) or "W" (4.30:1 traction-lok or Detroit Locker) that make the difference.