https://modesto.craigslist.org/pts/d/ford-428cj-cobra-jet-engine/6746066301.html
Photo 8 of 12 you can see that there’s a partial VIN stamp but you can’t quite make it out…
It’s too early to be a CJ block, unless you have one of the prototype 135 series Mustangs. Remember, there is no such thing as a special Cobra Jet block. The markings on that block are the same as any 428 Police car, a 428 T-Bird, or that of granny’s 428-4V station wagon. Or a GT500 (not KR) Shelby.
Royce, do you know what the earliest non 135 car CJ car was ?
Good info here:
https://www.428cobrajet.org/id-block
Let me know if that clears things up for you. 
After a thorough reading, I continue to be thoroughly mystified and confused.
All 50 of the 135 cars went down the line December 30, 1967.
There were a few pre - production cars built in January 1968, both Cougar and Mustang. I don’t know for sure but I expect a handful of Cyclones and Torino’s with the 428CJ would also have been built for press usage and display.
The block that you linked to undoubtedly has a VIN that will tell the tale of it being installed in a 428 powered something else.