Not to convolute this any further. Newer “Shelby GT’s” from 2006 up are factory produced Ford Mustang GT’s and are VIN’d that way. I have a 2016 Shelby Hertz and it is Titled and VIN’d as a Mustang GT. I had a 2007 Shelby GT-H as well and it too was Titled and VIN’d as a Mustang GT.
Not sure if the older ones are the same way.
Just my 2 cents
Ken
I think the issue here isn’t whether or not Shelby was a car manufacturer but which factory installed the 427. It’s clear that Ford did not install any 427 engines in Mustangs or Cougars in 1967. If Volkswagon purchased a 67 Cougar for research purposes and installed a 427 in it at their factory, would it be considered a factory installation? Sure, just not in a Ford factory which is what we all mean when we say factory installed. Just because some people want to claim a factory installation for their own purposes, primarily rarity and value, doesn’t make it so.
I agree with Jeff
No 427s from Ford in Mustangs or Shelbys in '67 and '68, even though they were listed in some 1968 marketing materials.
No Ford/Mercury installed 427s in '67 Cougars.
Ford/Mercury installed 427s in Cougars in 1968.
Been beat to death over at the SAAC Forum.
The 427 was the second engine in each of those three cars. They were originally manufactured with 428-8V engines in the San Jose assembly plant by Ford. Sure Shelby modified them after the fact - every Shelby was born a Mustang and modified into a Shelby. These three simply lost their original engines in the process.
None of this changes the fact that the OP has an error filled CAC report that does not describe what engine came in his car when it was built.
427s and Morrison’s Shelby can always pop up as a hot topic. Maybe CJ 4 speed Gs. as third. 
What happened to the 428-8V engines?
Shelby American was a manufacturer. From 1965 to 1967 Shelby Mustangs were equipped with their own Shelby serial number and manufacturing plate stating “manufactured by Shelby American, Los Angles, Ca”. My 67 Shelby has the Shelby number stamped into shock tower as well as the Shelby manufacturing plate. There was never a door tag or windshield tag. The Ford number is only stamped in the fender apron (which is covered by Shelby manufacturing tag), engine block, transmission. If Shelby American was not a manufacturer this would never be allowed by law.
Now when Ford took over Shelby production in 1968, the vehicle identification plate changed to Shelby Automotive. They have all the standard Ford identification tags and the Shelby number was added after the Ford serial number separated by a hyphen.
The 427 was listed as a factory option for the 67 GT500. Three were produced and documented.
Now to cover the VW comment. If Volkswagen purchased a Cougar it would have come from a Mercury dealer as delivered from factory. Purchased by Volkswagen and would not be a new car but a used car, and any modification would be a “day 2” modification, and would not have any documentation from the ORIGINAL manufacturer.
Now to cover the assumption that the engine born with the car on the Ford motor company assembly line is the only original engine regardless of factory documentation opens up a whole can of worms. Yes as the 3 GT500s were sent to Shelby American with 428s, every Shelby Mustang left San Jose as a running car and the Shelby factory optional engine was installed by the Shelby factory BEFORE the car was delivered to the dealer.
If you don’t agree then think about this. The Boss 429 Cougars were complete Rcode 428 cars delivered to Kar Kraft. The original factory engine being a Cobra Jet. Even though there is Factory documentation that they were strictly to be converted boss 9s, they would not be an original Boss 9 cars I guess. Would it be right to concourse restore one of the boss 9 Cougars to assembly line cobra jet specs? Of course not. Would it be right to restore your 67 Shelby to how it came from San Jose plant with no hood,nose,deck lid, lights, etc… of course not. These cars were intended to be high performance vehicles with options not offered on the production assembly line, but still factory builds. So many factory developmental cars were produced with different experimental options BEFORE the were sold to the public, It would be a shame not to recognize them.
You may not agree with me, but I’m just trying to educate people, that’s it! I may not know everything, but I am knowledgeable about a lot of things, especially the backgrounds of the cars I own and cars I have interest in. I have helped many forum members in the past and been helped by many forum members, that’s what we are here for.
I not going to debate this, it is information to EDUCATE, that’s it.
There is currently a 1965 Shelby GT 350 that was restored by Charles Turner to be a K code Mustang exactly as it was delivered to Shelby in 1965. Charles displayed the car at MCACN in 2019 along with all the restored Shelby components required to convert the car to a GT350. So yes, it would be cool if one could reunite one of those three Shelby GT500’s with its original 428 in a similar fashion. Or to see an early 1969 Boss 9 as it was delivered to KK - actually only a few came to KK with 428 SCJ engines, later cars came as “knock downs” without components that would be removed and discarded.
None of this changes the fact that the Op’s CAC letter is simply an error on the part of the worker who typed it
Yes, that was for that show, back to factory original now.
You are correct on the OP issue of having is clerical mistake.
