Have a copy of that same picture and a reported VIN. Car identified this picture is of a fairly low VIN though due to production issues its impossible IMHO to know when the car was really built and unfortunately don't have a copy from this car.
Not sure that CJ can be automatically thought of as something related to the 428CJ (or even original for certain) given how and where its applied. May be plant graffiti. Normally a rotation number is in that location from the ones I've seen and have collected. Does appear that there is another mark to the left of the picture. It's liklely the car line letter we find typically applied at Dearborn and San Jose in 69
To your original question. Is this normal/typical? IMHO no though the 8's have been found on some 69 Dearborn built Mustangs and Cougars in those locations. A few other 69 Boss 302's have had the 8 applied in other forward facing locations over the engine compartment black.
Its related to engine size, I believe, much like other years and plants in similar and other locations
